Practical Plant Genetics

CAIRO UNIVERSITY FACULTY OF SCIENCE

NEW PROGRAM

Biotechnology/BioMolecular Chemistry

COURSE TITLE:

PLANT AND ANIMAL GENETICS

COURSE CODE:

BIO Bi 112

INSTRUCTOR:

Dr. Tarek Kapiel

[Plant Genetics]

[email protected]

LAB: Sunday: 11:00 – 14:00

COURSE WEBPAGE ADDRESSES:

http://www.dnai.org/lesson/go/19619/http://groups.yahoo.com/group/CU-BIOTECH

[email protected]

LEVEL:

1 (2nd semester)

CREDIT: [Practical 1 (1X3 hr/wk)]

SPRING 2007

mailto:[email protected]

http://www.dnai.org/lesson/go/19619/

http://groups.yahoo.com/group/CU-BIOTECH


Dr. Tarek Kapiel Practical Plant Genetics

DNA & DNA Extraction LAB 1

1

DNA and DNA Extraction

See and touch the hereditary molecules

Overview

This lab discusses what DNA is and how it relates to genes

and chromosomes. How and why DNA is extracted in the

genetic engineering process is also covered.

At the completion of this lesson, you should be able to:

Visualize the relationship between DNA, genes, and

chromosomes.

Compare the roles that DNA and proteins play in a cell.

Contrast DNA and proteins in their chemical make up.

Explain why DNA extraction is important in genetic

engineering and how it is done.

Understand why genes can be transferred between

organisms and still work.

Objectives:

1- To isolate nucleic acids (DNA and RNA).

2- To understand the importance of DNA.

Background:

Deoxyribonucleic acid (DNA) is the genetic material present

in all organisms, from bacteria to humans. DNA is the

material that makes up genes.

DNA is the instruction manual for living things. Within the

relatively simple double helix structure, DNA holds the coded



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information for how to make every protein a living organism

might need throughout its entire life.

Very pure DNA can be easily extracted from cells in a

research laboratory. DNA is a non-living stable molecule. The

DNA code is universal allowing it to work the same in all

living things. This is a critical fact that makes genetic

engineering possible. Genetic engineering is the directed

addition of new DNA to an organism's genetic makeup, its

genome. Once scientists understood the properties of DNA

and how it functions as genetic material, they could envision

and invent techniques for genetic engineering.

DNA extraction is necessary because genetic engineers need

to be able to work with the DNA, cut it, locate and clone a

single gene, and modify the gene before they insert it into

another organism.

DNA is composed of nucleotides bonded to a sugar-

phosphate backbone. Double stranded DNA forms a double

helix structure.

The DNA double helix coils up into compact structures called

chromosomes. Small segments of the chromosome that

encode a single protein are called genes.

Chromosomes are microscopic. There are thousands of genes

on each chromosome and hundreds of nucleotides in the

DNA sequence of each gene.

The role of DNA is to store and pass on genetic information.

The sequence of DNA subunits determines an organism's

traits.



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Dna Structure

DNA has a double helix structure composed of nucleotides.

DNA is a macro molecule that consists of many subunits

connected together. The subunits are called nucleotides.

Each nucleotide has three parts; a sugar, a phosphate, and a

base. The sugar and phosphate molecules are linked together

in two long chains. The bases are linked to the sugar-

phosphates. Bases of one strand are bound to those of the

other strand by hydrogen bonds making what is called a base

pair. The structure of DNA is a double helix which allows it to

perform the functions of replication and information storage.

Base pairs look similar to rungs on a ladder. In fact, the DNA

structure could be described as a long ladder twisted into a

spiral.


There are only 4 nucleotides in DNA, Adenine (A), Guanine

(G), Thymine (T), and Cystosine (C). The chemical structures

of Thymine and Cytosine are smaller, while those of Adenine

and Guanine are larger. Size and structure of the specific

nucleotides cause Adenine and Thymine to always pair



4

together while Cytosine and Guanine always pair together.

Therefore the two strands of DNA are considered

complimentary.

Simple Extraction of DNA from Peas

The plant tissue must be ground with a mortar and pestle to

break the plant cells open allowing the DNA to freely leave

the cell.

Why is it necessary to extract the DNA out of a cell in genetic

engineering? As mentioned above, DNA is found in the

nucleus of a cell. In order for genetic engineers to be able to

work with and transfer DNA into another organism, it must

be first taken out of the cell. Fortunately, a DNA molecule

remains somewhat stable outside of a living cell allowing

scientists the opportunity to work with and study it without

destroying it. To extract DNA, tissue samples are taken from

plants, and crushed to break open the cells.

Next, a buffered salt water solution is added into which DNA

dissolves easily. The DNA is purified by adding an organic

solution into which other molecules, such as fats and

proteins dissolve. The purified DNA solution is separated off

and the DNA is precipitated out of the solution by adding

alcohol. The DNA is now a solid string that can be spooled

out with a hook. The extracted DNA is placed into test tubes

with a weak buffer solution and can be stored almost

indefinitely.

During DNA extractions, the entire cells' DNA is extracted at

the same time. Extracted DNA has usually been sheared into

smaller pieces due to the leaf tissue grinding process. This

makes it difficult to isolate an entire chromosome in once

continuous strand. However, large pieces that contain several

to dozens of genes can be extracted intact with this method.



5

After isolating the DNA, researchers can use it for further

laboratory studies including genetic engineering.

Materials:

1. Peas, about 50 g (frozen ones are suitable, but thaw them

first)

2. SDS solution (sodium dodecyl sulfate) or washing-up liquid,

(dishwashing liquid solution) 10 cm3 (ml).

3. NaCl (Table Salt), 3 g.

4. Distilled water, 90 cm3.

5. Very cold ethanol, about 10 cm3, straight from the freezer.

6. Novozymes Neutrase® (a protease), 2–3 drops.

7. Ice with cold water.

8. Filter paper.

9. Large funnel.

Procedure:

1. Dissolve the salt in 90 cm3 of distilled water. Add the

washing-up liquid and mix gently.

2. Mash the peas using a glass rod or a spoon. Add the pea pulp

to a beaker with the salty washing-up liquid solution.

3. Stand the beaker in a water bath at 60 °C for exactly 15

minutes.

4. Cool the mixture by placing the beaker in an ice water bath

for 5 minutes, stirring frequently.

5. OPTIONAL: Pour the mixture into a blender and blend it

for no more than 5 seconds.

6. Filter the mixture into a second beaker. Ensure that any foam

on top of the liquid does not contaminate the filtrate.



6

7. OPTIONAL: Add 2–3 drops of protease to about 10 cm3 of

the pea extract in a boiling tube and mix well.

8. Very carefully pour ice cold ethanol down the side of the

boiling tube, to form a layer on top of the pea extract.

9. Leave the tube, undisturbed, for a few minutes.

10. Nucleic acids (DNA and RNA) will precipitate into the upper

(ethanol) layer


break the plant cells open allowing the DNA

to freely leave the cell.



7



8

Expected Results

A slimy white material will precipitate at the interface of the

ethanol and filtrate layers. This material consists of clumped-

together DNA strands.

Extracted soybean DNA after it has precipitated out of solution.

What's Going On?

The procedure used in this activity has the same essential

elements as more advanced laboratory DNA extraction

procedures: mechanical and thermal disruption of cells,

liberation of the DNA, and precipitation of the DNA.

In this procedure, the Pea cell walls are broken down by the

mechanical mashing and then the heating, and the detergent

dissolves the lipids in the cell membranes and nuclear

envelope. The DNA is no longer confined inside the nuclear

membranes. It is highly soluble in water because the

phosphate group of each nucleotide carries a negative charge.

However, the positively charged sodium ions from the salt in

the extraction solution are attracted to the negatively charged

phosphate groups on the DNA backbone, effectively



9

neutralizing the DNA's electric charge. This neutralization

allows the DNA molecules to aggregate with one another.

When the ethanol is added, the DNA clumps together and

precipitates at the water/ethanol interface because the DNA

is not soluble in ethanol.

Each glob of material in the precipitate will contain millions

of DNA strands clumped together, along with some of the

protein that is normally associated with DNA. Fortunately, a

DNA molecule remains somewhat stable outside of a living

cell allowing scientists the opportunity to work with and

study it without destroying it.

DNA Facts

All DNA is folded and packed into the nucleus of a human

cell. The diameter of the nucleus is about 0.005 mm or 1/500

the width of a dime.

There are 6 billion bits of information coded by DNA in each

of our nucleated cells (a bit is a measure of information).

Each human cell contains twenty-one times the information

that is found in the Encyclopedia Britannica, which is

thought to have about 280 million letters.

There are about 3 x 109 nucleotide base pairs in the human

genome (the complete set of genes in one cell). If you lay all

the DNA strands from a single human cell end to end, it

would be about 2 meters long!

Calculate how many times to the moon and back a human's

DNA would reach if it was removed from each cell and each

strand laid end-to-end. Here is the information you need:

Each cell nucleus in a human holds about 2 meters of DNA

and a typical adult human is composed of 60 trillion cells.

The distance from the earth to the moon is 380,000

kilometers.



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Student Worksheet DNA and DNA Extraction


Name: ____________________ ID#:__________ DATE: __/4/2007

1. From where, and why, do scientists extract DNA? Give several

examples. ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

2. What is the function of DNA? ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

3. Where is DNA located?

______________________________________________________

______________________________________________________

4. Most of the bases in our DNA are (Circle one): a. coding b.non-coding 5. Below is a portion of a DNA strand. Fill in the blanks with the complementary base pairs.

A T T G C C C A A T A G G C

__ __ __ __ __ __ __ __ __ __ __ __ __ __

6. A sequence of DNA that codes for the production of a specific protein is called a: ______________________________________________________

______________________________________________________

7. State your results after observing your DNA. Do you think you have pure DNA? Why or why not? ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________



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8. What does the salt do?

______________________________________________________

______________________________________________________

______________________________________________________

9. What does the blender do? ______________________________________________________

10. When you mix the blended cell source with the SDS (Soap),

what is happening? ______________________________________________________

______________________________________________________

______________________________________________________

11. What does the alcohol do? Why does the DNA rise to the top

after adding alcohol? ______________________________________________________

______________________________________________________

______________________________________________________

12. In the space below, draw what you saw in the test tube. Make

sure to label the solutions, the interface layer, and the DNA. ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

13. Why can’t you see the double helix? ______________________________________________________

______________________________________________________

______________________________________________________

14. What part of the cell did the DNA come from? ______________________________________________________

______________________________________________________

______________________________________________________

15. When we extracted DNA from 10 different fruits and

vegetables, we noticed that there was a lot of variation in the

amounts of DNA yielded from each. Why do some plants give

more DNA than others? ______________________________________________________

______________________________________________________

______________________________________________________



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16. In the space below, draw a simple model of DNA. Make sure to

label the bases correctly. ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

17. Some people are concerned that we are able to manipulate the

DNA of crop plants and that it will change them into something

that they are not. Can you give some examples of the types of plant

genes that might be changed? Do you think that scientists should

proceed with this type of research? Why or why not? ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Practical

Plant Genetics

By:

Dr. Tarek Kapiel, B.Sc. M.Sc., Ph.D. Associate Professor (Lecturer)

Cytology and Genetics Division Botany Department,

Faculty of Science, Cairo University.

[email protected]

©2009 All rights reserved

mailto:[email protected]�


MITOSIS in Plant Cells LAB 2

2

Eukaryotic Cell Division

MITOSIS in Plant Cells

Objectives:

1. Students will prepare r oot t ip s quashes t o o bserve mitosis in onion roots. 2. Students will identify the various stages of mitosis in onion root tips. 3. Students w ill dr aw e ach phase of mitosis a nd t he main characteristics of each stage. 4. Students w ill observe h ow sa lt ( NaCl) a nd c olchicine a ffects mitosis in onion roots and they will study the effect of salt NaCl on the duration of each stage of mitosis.

Background:

Eukaryotes are diploid, which means they have two sets of chromosomes; o ne se t o f c hromosomes i s i nherited f rom each p arent. Eukaryotic DNA is enclosed by a nuclear envelope. The p roper s orting a nd distribution o f multiple chromosomes during cell division i s a complex p rocess t hat requires the temporary dissolution of the nuclear envelope. There are t wo t ypes o f cell d ivision i n eukaryotes, M ITOSIS and ME IOSIS, a nd they ha ve v ery different f unctions. Mitosis i s d esigned t o i ncrease t he n umber of c ells, a nd t o ensure that each of the daughter cells is genetically identical, containing t he di ploid ( 2n) number of c hromosomes. B y contrast, meiosis i s responsible for c onverting a di ploid c ell



3

(i.e a cell c arrying t wo complete sets of chromosomes) into four h aploid (1n) c ells, e ach c arrying onl y one s et of chromosomes. Eukaryotic organisms carry out mitosis throughout t heir entire l ife t o g row and t o r eplace ol d or damaged cells. S ome eukaryotic organisms u se m itosis to reproduce asexually. The d aughter c ells produced b y mitosis a re diploid and genetically i dentical to each other and t he parent cells that produced them. The g rowth of multicellular or ganisms depends on Uprecise replicationU of i ndividual c ells f ollowed by Ucell d ivisionU. During r eplication, e ukaryotic ce lls g o t hrough Uan or dered series o f c yclical e ventsU. T he t ime f rom o ne c ell d ivision t o the next is called a Ucell cycleU. The c ell c ycle h as t wo m ain p hases, UinterphaseU and UmitosisU. Interphase i s f urther di vided i nto t hree distinct phases: G1 (gap 1 ), S (DNA s ynthesis, l asting 6 –8 ho urs i n eukaryotic c ells, a t t he e nd of w hich t he chromosomes h ave been duplicated), and G2 (gap 2, lasting about 4 hours) and Mitosis (M) Uis the phase of actual divisionU.

CELL CYCLE = INTERPHASE + MITOSIS

Cells only spend a small part of their l ife dividing. The time between consecutive mitotic divisions i s r eferred t o a s interphase. Eucaryotic c ells sp end most o f t heir t ime i n interphase. During interphase the cell’s genetic material is in the form of chromatin (uncoiled DNA), nucleoli are present, and the n uclear e nvelope i s clearly v isible. S hortly b efore mitosis, the cell duplicates its DNA during the S (synthesis) phase of interphase.



4

• Cell Cycle

Mitosis is the process by which a cell ensures each daughter cell will have a complete set of chromosomes.

Mitosis occurs in five stages:

1. UInterphase:

The Ustart of mitosisU, the DNA of each chromosome UreplicatesU. Each chromosome t hen r eorganizes i nto paired s tructures called sister chromatids, w ith each m ember of t he pair containing a Ufull co py o f t he D NA s equenceU. I n e arly interphase t he i ndividual c hromosomal st ructures b ecome



5

invisible. I nterphase c hromosomes a re c alled Uchromatin U (Flemming 1 879), i .e., n uclear st ructures st ainable b y b asic dyes. Nuclear material is surrounded by a nuclear envelope. Dark-staining b odies, n ucleoli, are visible. C hromosomes a ppear only as dark granules within the nucleus. The chromosomes are n ot i ndividually d istinguishable b ecause t hey a re uncoiled into long, thin strands.

2. UProphase:

Nuclear e nvelope a nd nucleoli d isappear. Chromatin condenses i nto c hromosomes, w hich b egin t o c oil a nd become distinguishable thin, threadlike structures. They are made up o f tw o id entical s ister chromatids. The si ster chromatids c ondense, thickening u ntil they appear joined a t a single site, known as the centromere. The mitotic spindle forms and begins t o move chromosomes t owards t he center of the cell.

3. UMetaphase: The si ster chromatids l ine up i n t he m iddle (equatorial plane) of the cell. A metaphase chromosome consists of two chromatids ( sister chromatids) and t he centromere, which holds them together. The centromere may divide each of th e chromatids i nto tw o chromosome arms. Th e regions at both ends of the chromosome are the telomeres. The m itotic spindle i s f ully f ormed. S pindle f ibers a re attached to centromeres and extend to the poles of the cell. The p oint o f attachment to the m itotic s pindle fibers is th e kinetochore. During m etaphase, c hromosomes c an be visualized u nder th e l ight m icroscope a s d iscrete e longated structures, 3–7 μm long.

4. UAnaphase:



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The chromatid pairs (Sister chromatids) split apart at the centromere, begin t o s eparate, becoming i ndividual chromosomes, ( Each f ormer c hromatid i s n ow a chromosome) whi ch begin t o m igrate t o toward o pposite poles (ends) of the cells.

5. UTelophase:

The final stage of mitosis, a full set of chromosomes reaches each pole of the cell. The mitotic spindle begins to disappear. The n ucleus and n ucleoli b egin t o r eappear. A n uclear membrane f orms around the chromosomes a t each p ole o f the cell. Chromosomes begin to unravel into chromatin.

Mitosis ends with the formation of two new cells, each with a matching full set of chromosomes.

UCytokinesis

Cytoplasmic division usually occurs a t t he e nd of t elophase. The c ytoplasm d ivides; t he c ell m embrane p inches i nward ultimately producing two daughter cells (Cytokinesis). Eukaryotic cells g o t hrough c ell d ivision cycles ( cell c ycle). Mitosis (M) in eukaryotic cells lasts about an h our. This is followed b y a p hase, G1 (interphase), o f e xtremely v aried duration. In plant cells cytokinesis is accomplished by the formation of a Ucell plateU.

Plant mitosis. Onion (Allium) root-tip

Allium Root

Examine l ongitudinal s ections of s prouting Allium root-tip. The onion root tip is protected by a root cap that is constantly



7

worn a way a s t he root pushes t hrough the s oil. Behind t he root c ap is th e r egion of d ividing c ells ( the a pical r oot meristem). Farther back from the tip, cells cease dividing and begin e longation and di fferentiation. W ith l ow, a nd then medium powers, locate the region of dividing cells. The plane of division of these cells is most commonly at right angles to the long axis of the root. Thus, longitudinal sections through the r oot r esult m ost o ften i n si de views o f t he m itotic apparatus, r ather than d iagonal or polar v iews t hus making interpretation e asier. T he d iploid number of c hromosomes (two se ts -- one f rom t he m ale a nd one f rom the f emale parent) in this species of onion is 16.

root cap

Region of Division

Region of Elongation and Differentiation

Allium Root Tip

With high power magnification, identify the stages described below and label. Note that mitosis is a continuous process. The cells you will see o n permanent sl ide mounts h ave n ot a lways b een "captured" and s topped i n e xactly t he s ame m oments of development t hat you're textbook a nd lab i llustrations show as representative of a certain phase.



8

• Stages of Mitosis in Plant Cell



9

Materials:

1. Students will set up their own slides.

2. Compound light microscope

3. Prepared onion or broad bean root tip slides.

4. Microscope slides and coverslips

5. 45% acetic acid

6. Glass rods

7. Razor blades

8. Paper towels

9. UMaterials needed per slide are:U fresh grown onion r oot

tip, 5-10ml d istilled w ater, 5ml 6M HC l, 1ml Feulgen

reagent i n a v ial, 5ml 4 5% a cetic a cid, d ropper pipette pe r

solution, beaker, slide, coverslip, and a pencil with eraser or

small c ork t o s quash t he sl ide, 5-10ml C arnoy's s olution

(1 glacial a cetic a cid: 3 absolute alcohol) i n v ial a nd

toothpicks.

Procedure:

1. Take an ordinary onion. Cut off any old root growth. Place

the oni on i n a cup of w ater s o t hat o nly t he r oot p ortion i s

under water. T o do this, push toothpicks into the side of the

onion w hich e xtend o utward a nd h old i t o n t he r im of t he

cup. New roots should grow within two days.

2. Cut off 0.5-1 cm of growth at the root tip.

3. Transfer i mmediately t o C arnoy's s olution. A fter 2 4 h ours,

roots should be stored in 70% ethanol in a refrigerator. This

stops cell division.



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4. After obtaining the root tip, pour off the fixative and replace

it with 2-5 ml distilled water. Solutions may be poured into a

beaker or down the drain.

5. After 1 minute remove the w ater with a pipette and add 2-5

ml 6M HCl.

6. After 3 minutes carefully remove the acid and wash tissue off

with distilled water. Agitate the vial for 1-2 minutes. Discard

the water.

7. Use forceps to transfer the tissue to a vial containing 1-2 ml

Feulgen r eagent. T he r eagent m ay be a dded t o t his v ial i f

desired. ( UCAUTION:U this dye w ill s tain h ands and clothes

permanently).

8. After 2 0-30 m inutes u se f orceps t o t ransfer t he tissue t o a

vial containing 5 ml 45% acetic acid.

9. Place 1 -2 drops of acetic a cid ont o a m icroscope s lide a nd

transfer t he t issue t o t he drop. U sing d issecting p ins a nd

razor blades macerate the tissue into tiny pieces.

10. Place a coverslip over the m acerated tissue trying not t o get

air bubbles under the coverslip. Press down firmly onto the

coverslip with a small cork or pencil eraser to spread the cells

in a very thin layer. P ush down in a perpendicular direction

and the coverslip should not break.

11. Examine u nder l ow p ower. Scan u nder l ow p ower (10 x

objective) to look for areas with cells undergoing mitosis, and

then examine under high power (40 x objective). Try to find

all the stages of mitosis.

12. Draw a ll t he d ifferent v iews o f c ells p resent under h igh

power.

13. After y ou h ave s tudied the section, y our in structor w ill test

your ability to recognize the stages of mitosis.



11

Onion bulb supported by tripod of toothpicks in a beaker of water. Roots can be removed and actively growing root tips squashed and

examined for cell mitosis.



12

UStudent Worksheet [LAB 2]

Eukaryotic Cell Division MITOSIS in Plant Cells

Name: ___________________ ID#:__________ DATE: U /4/2007 1. Examine the prepared slide with stained longitudinal sections of

the r oot a pical m eristem. First sc an t he sl ide w ith low power (10 x objective lens). The end of the root is protected by a root cap. What is the shape of the root cap?

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

2. Right behind the root cap is the meristem, where there is active cell d ivision. Now shift t o the high power (40 x objective l ens) objective a nd f ind c ells in ea ch s tage o f m itosis. S tudy the section carefully. A re m ost o f the cells di viding, or is th e majority in interphase?

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

3. Examine your sample of microscope slides of plant cells (onion root tip s) under t he m icroscope. Most o f t he c ells w ill b e i n interphase (between cell d ivisions). U sing y our microscope, scan the slides to find each one of the four stages of mitosis.

4. UDraw a schematic representation of y our observations a t e ach stage in the space provided below.

5. Indicate a nd UclearlyU label t he i mportant f eatures o r e vents o f each st age. [The di ploid n umber of chromosomes o f O nion (Allium) Root Tip is 16].

6. Looking along the rows of cells, identify what stage each cell is in. Use the photos below as a guide.



13

UStages of Mitosis

Hiacinthus Narcissus Your Sample

7. Use the data table to record the number of cells that you see in each of the stages.

Stage of Cell Cycle Number of cells in the Stage: Interphase

Prophase

Metaphase

Anaphase

Telophase



14

Low Power Magnification: ______X High Power Magnification: ______X

Interphase

Prophase

Metaphase

Anaphase

Telophase



15

Observing Mitosis in Onion Root Tip cells

1. Before this lab, Onion bulbs were transferred to either an aerated solution of salt or an aerated solution of water for three or more days. Stain the root tips will stain the DNA of the Onion root tips. Your job is to prepare a “squash” of the Salt-treated and Water-treated root tips and observe the differences.

2. Place a water-treated root tip on a clean slide. Separate the intensely pink terminal end from the relatively unstained portion leaving 0.25-0.5 cm of intensely pink root tip on your slide.

3. Carefully macerate the root tip by tapping up and down with the

rounded end of a glass rod. Place a folded paper towel on top of the coverslip. Squeeze out the excess moisture by gently drawing the index finger of one hand across the paper towel, while holding onto the edge with your other hand. When the tissue has been broken into small fragments, lower a cover slip onto the preparation.

4. Flatten the tissue on the slide by placing your thumb on the paper

towel over the coverslip and gradually increasing pressure. Roll your thumb from side to side gently increasing the pressure with each roll. Avoid sliding the coverslip from side to side. Press down with the eraser end of your pencil to complete the squash.

5. Remove the paper towel and examine your root tip under the microscope. A well-made squash will have a monolayer of well-separated cells, with only a few larger chunks of tissue.

6. Find a cell in metaphase, in which the chromosomes are clearly

separated, using either your slide or another person’s slide. Using high power, observe the cell.

7. Using high power, count the number of nuclei visible in a high power field and record your answer.

8. In the same field, count the number of cells in each of these phases: prophase, metaphase, anaphase and telophase. Record your results.

9. Like a snapshot, the prepared onion root tip slide catches cells in

various stages of mitosis.



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10. The probability of finding a cell in a certain stage of mitosis is proportional to the length of the time a cell remains in that stage. If we know how frequently onion root tip cells divide, then we can calculate the duration of each stage of mitosis. Scientists have determined that the control system governing cellular reproduction dictate that onion root tip cells divide every 24 hours. In other words the cycle duration is 1440 minutes. Calculate the duration of each phase of mitosis using the following formula:

OR: Number of minutes in the stage =

% of cells in the stage X

1440 minutes

11. Calculate the t ime f or e ach st age a nd f ill i n t he t able b elow;

then check your answer.

12. Inspect 100-200 cells and count the number of cells in prophase, metaphase, anaphase, and telophase. URecordU your results and the pooled class results in your assignment.

13. Repeat the previous steps for a root tips treated with salt. Inspect 100-

200 cells and count the number of cells in prophase, metaphase, anaphase, and telophase. URecordU the results from your observation of the onion root tip slide and transcribe the pooled results from your lab



17

section into the column labeled pooled results. Then calculate the duration of each phase of mitosis using the pooled results.

14. Compare the duration of each phase of mitosis to that reported in

scientific literature for onion root tip (prophase = 133 minutes, metaphase = 22.9 minutes; anaphase- 14.1 minutes, telophase = 20.5 minutes). Are your results similar? What might explain differences you observed between your lab section’s results and that reported in scientific literature? What reasons might exist for the varying length of each phase of mitosis?

Observing Mitosis in Salt-Treated Onion Root Tips

1. Inspect 100-200 root tip nuclei. Count the number of cells in each

stage of mitosis for both root tips aerated with water, and root tips aerated with Salt. Transcribe your class’ results into the following table:

2. Describe the differences you observed in the treated root tips with

salt. Explain how treatment with salt affects root tips. _________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________



18

Analysis & Conclusions: 1. What stage were the majority of the cells in? _________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

2. The onion plant began as a single cell. That cell had X number of chromosomes. How many chromosomes are in each of the cells that you observed? (Give the answer in terms of X.) How do you know?

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

3. If this onion would reproduce sexually, it would need to produce sperm and/or eggs by the process of meiosis. After meiosis, how many chromosomes would be in each sex cell (in terms of X)?

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

4. If this onion would complete the process of sexual reproduction (fertilizing an egg cell), how many chromosomes would be in the zygotes that are produced (in terms of X)?

_________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________

Practical

Plant Genetics

By:




[email protected]




Meiosis in Plant Cells

LAB 3

2


MEIOSIS in Plant Cells

Objectives:

1. To identify cells in all stages of meiosis on prepared

microscope slides, diagrams, and photographs.

2. To describe the behavior of chromosomes during all

phases of meiosis.

3. To be able to define the following terms: anaphase,

autosome, centromere, chromatid, metaphase, nucleus,

prophase, gametogenesis, somatic, spindle, synapsis,

telophase, tetrad, karyokinesis, cytokinesis.

Background:

In most species, it is very important that the offspring

produced by fertilization have the same number of

chromosomes as the parents. Meiosis is a special type of cell

division that produces haploid gametes. Meiosis involves two

cell divisions and ultimately produces four haploid gametes.

Meiosis involves two consecutive divisions of a particular cell

type, which results in four daughter cells that have half of the

chromosome number of their mother cell. The daughter cells

are thus genetically different from the mother cell, and

due to independent, random assortment of chromosomes

and crossing over, they are genetically different from one

another as well.



LAB 3

3

The first division is called the reduction division, since

this is the one during which chromosome number in the cells

is reduced.

Only certain types of cells divide by meiosis that occurs in the

archegonium/antheridium in plants, and in the gonads in

animals. Cells with an odd number of chromosome sets

normally cannot carry out meiosis, as chromosome pairing is

messed up.

The haploid gametes produced by meiosis are different from

each other as well as from the parent cells due to the

crossing over of genetic material between homologous

chromosomes and the random distribution of

homologous chromosomes.

In meiosis, one homologue of each chromosome type is

distributed to each of the resulting "daughter" nuclei. The

two resulting nuclei are not identical, and have one-half the

original chromosome complement. Meiosis occurs during

the process of gametogenesis (the production of gametes),

where haploid spores are produced that divide mitotically

to form the gametophyte. The somatic chromosome

complement is restored when the haploid sperm nucleus

fuses with the egg nucleus during fertilization.

The behavior of the chromosomes during meiosis is known to

be responsible for the segregation and independent

assortment of alleles.



LAB 3

4

STAGES OF MEIOSIS

MEIOSIS I: Reductive Division (Diploid Haploid)

Prophase I:

Similar to prophase of mitosis with one important difference:

Crossing Over: Pairs of homologous chromosomes

synapse together to form tetrads and exchange genetic

information (DNA). Crossing over creates new, recombinant

chromosomes.

Homologous chromosomes code for the same genetic

information and are of the same size, but are different

because one comes from an individual’s mother, while the

other comes from the individual’s father.

Metaphase I:

Brief stage in which tetrads line up in the equatorial plane

of the cell.

Anaphase I:

Homologous chromosomes separate and migrate to opposite

ends of cell.

Telophase I:

A full set of chromosomes reaches each pole of the cell.

The cells produced are haploid, only contain half of the

original number of chromosomes.

Interphase

May be very brief or absent between meiosis I and meiosis II.

MEIOSIS II:

Very similar to mitosis.



LAB 3

5

Prophase II:

DNA condenses into chromosomes. No crossing over occurs.

Metaphase II:

Individual chromosomes line up in the equatorial plane of

the cell.

Anaphase II:

Chromatids separate and begin to migrate to opposite poles

of the cell.

Telophase II and Cytokinesis:

A full set of chromosomes reaches each pole of the cell. Four

different gametes are produced.



LAB 3

6



Stages of Meiosis during Pollen Formation in the Flower of a Lily



LAB 3

7



LAB 3

8

Materials:

1. Plants with immature inflorescences or flowers

2. Compound microscope

3. Forceps with curved tip

4. Dissecting needles (bent end preferred)

5. Microscope slides

6. Cover glasses

7. Stains (acetoorcein and/or Wittmann's hematoxylin acetic

acid)

8. Paper towels

9. Lens paper

Procedure:

1. Obtain an unopened inflorescence from the material

provided, and remove the paperlike covering to expose the

developing buds.

2. Transfer a few (three or four) of these buds to a microscope

slide.

3. Add a drop of stain (either aceto orcein or Wittmann's

hematoxylin). If too much stain is added, simply blot some of

it away. Be sure to include one or more very small buds.

Larger buds will probably contain only pollen grains because

the sporogenous tissue will have completed meiosis.

4. Microspores and pollen grains should be seen, but it is likely

they will be found even in some of the smaller buds, so it is

best to start with the smaller buds and include larger buds as

needed.

5. Use a dissecting needle or forceps to crush the buds in the

stain. This will release microspore mother cells from the



LAB 3

9

anthers. Repeated tapping of the buds with the needle may

be necessary to release sufficient numbers of microspore

mother cells from the anthers.

6. Use the forceps and/or dissecting needles to remove as much

of the debris as possible. Even small pieces of petals prevent

the cover glass from lying flat and will lead to a distorted

image when viewed with the microscope.

7. If hematoxylin is used, a drop of 45% acetic acid should be

added to destain the cells.

8. Add a cover glass. It may be necessary to add more stain or a

drop of 45% acetic acid to the preparation in order to make

the cover glass lie flat.

9. Blot away the excess liquid, but be careful to avoid adding

very much pressure to the cover glass because the

chromosomes are somewhat fragile.

10. Observe the slide at low and high dry magnifications. Do not

try to use oil immersion at this time. Once the preparation is

scanned with the compound microscope, it may be obvious

that some pressure on the cover glass is needed in order to

spread the arms of the chromosomes.

11. Use oil immersion microscopy for detailed observation of

good representative stages.

Observations

A wide range of cell types may be observed. Some non-

meiotic cells will be seen. Non-meiotic cells will resemble

onion root tip cells or other undifferentiated cells. Cells

undergoing meiosis will be larger than the cells of the

supportive tissue and will contain prominent nuclei or

obvious chromosomes. If very small buds are used,

premeiotic mitotic figures will be observed in what will



LAB 3

10

become microspore mother cells. Meiosis is typically divided

into the following stages:

Meiosis I

Leptotene:

Chromosomes become visible as threads. Keep in mind that

what appears to be a single thread is actually two chromatids

because replication took place in the interphase prior to

meiosis.

It may be necessary to force the cover glass down a bit in

order to make individual chromosomes visible.

Zygotene:

Pairing of homologous chromosomes occurs. The

chromosomes appear thicker and less numerous because

pairing occurs. Again, it may be necessary to apply some

pressure to the cover glass in order to observe the paired

nature of the chromosomes.

Pachytene:

The chromosomes become shorter and thicker. The amount

of chromosomal material appears to be considerably less

because the chromosomes have become much shorter. The

fact that the chromosomes are paired should be obvious.

Diplotene:

The characteristic feature of diplotene is the presence of

chiasmata. The chromosomes are also shorter

than in pachytene.

Diakinesis:

Repulsion of the centromeres and terminalization of the

chiasmata mark this stage. The chromosomes are very short

and thick, but they have not yet lined up in a characteristic

metaphase figure.

Metaphase I: The chromosomes are lined up on the spindle. The staining

procedure used here does not reveal the spindle. A polar view

of metaphase I reveals the chromosomes to be organized at

one plane in the cell. A nonpolar view of metaphase I makes

it appear as though the chromosomes are lined up across the

middle of the cell.



LAB 3

11

Anaphase I: Separation of the paired homologs. It should be noted that

the chromosomes now appear thinner.

Comparisons with metaphase I make it obvious there has

been a halving of the genetic material with half going to each

pole. Early and late stages of anaphase I will be seen.

Telophase I: Once the chromosomes have moved to the poles in anaphase,

they begin to lose their identity and become reorganized into

the nucleus. This marks telophase.

Interphase: There is a brief period when the microspore mother cells

appear to contain two interphase nuclei. Because this is a

brief part of meiosis this interphase may not be seen by every

laboratory class. In some species, the chromosomes seem to

go directly from telophase I into prophase II.

Meiosis II

Prophase II:

Chromosomes become visible as long threads. Note that this

occurs in both of the nuclei of the microspore mother cell.

Metaphase II: The chromosomes become aligned on the spindle apparatus.

Note that different cells present different configurations

depending on the angles from which they are observed.

Anaphase II: Separation of the replicated chromatids. Compare the

number of chromosomes and the thickness of the

chromosomes with what was observed in anaphase I.

Telophase II: The chromosomes lose their distinctiveness and become

organized into nuclei. Note that there will be four haploid

nuclei within the confines of what started out as a single

diploid cell.

Tetrad:



LAB 3

12

The original microspore mother cell has been divided into

four cells. A polar view of these cells resembles an orange

with four sections which has been cut through the equator. A

non-polar view of the tetrad may be difficult to focus because

the “orange sections” appear to be piled on top of each other.

Microspores: The uninucleate haploid tetrads are released, and at this

stage are called microspores.

Pollen grains: These result from a mitotic division within the microspores.

Stages typical of mitosis can be seen including prophase,

metaphase, anaphase, and telophase. Cytokinesis may also be

seen. Because of the shape of the microspores, views of

metaphase are more often polar than nonpolar, making it

possible to count all eight chromosomes, but the same shape

makes it difficult to distinguish anaphase from telophase

since one generally finds polar views of these stages as well.

The resulting pollen grains are bicellular and have distinctive

wall markings.

This lab lends itself very well to encouraging students to

share what they have found with others. If they have found

something worth showing to others, they should announce

what they have to share and go see the stages others have

found. In this way, a few preparations per student can result

in a whole array of meiotic figures for all to see. Students

should also compare the stages they have observed with the

figures on display.



LAB 3

13

Student Worksheet [LAB 3]



Name: ___________________ ID#:__________ DATE: /4/2007

1. Examine the prepared slide with stained sections of lily anthers.

First scan the slide with low power (10 x objective lens), the by

using the high power (40-100 x objective lens).

2. Stages of Meiosis:

Meiosis I

Low Power

Magnification: ______X

High Power

Magnification: ______X

1. Leptotene:

2. Zygotene:

3. Pachytene:



LAB 3

14

4. Diplotene:

5. Diakinesis:

6. Metaphase I:

7. Anaphase I:

8. Telophase I:



LAB 3

15

9. Interphase:

Meiosis II

10. Prophase:

II

11. Metaphase:

II

12. Anaphase:

II

13. Telophase:

II



LAB 3

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Meiosis in Lily

English name: A lily Scientific name: Lilium grandiflorum Familia: Liliaceae Classis: Monocotyledonas Phylum: Angiospermae Regnum: Plantae

Meiosis results in 4 haploid cells that are each unique in its genetical content



LAB 3

17

Practical

Plant Genetics

By:




[email protected]



r. Tarek Kapiel Practical Plant Genetics

DNA Extraction LAB 4

2

DNA Extraction


overview

This lab discusses what DNA is and how it relates to genes

and chromosomes. How and why DNA is extracted in the

genetic engineering process is also covered.

At the completion of this lesson, you should be able to:

Visualize the relationship between DNA, genes, and

chromosomes.

Compare the roles that DNA and proteins play in a cell.

Contrast DNA and proteins in their chemical make up.

Explain why DNA extraction is important in genetic

engineering and how it is done.

Understand why genes can be transferred between

organisms and still work.

Objectives:

1- To isolate nucleic acids (DNA and RNA).

2- To understand the importance of DNA.

Background:

Deoxyribonucleic acid (DNA) is the genetic material present

in all organisms, from bacteria to humans. DNA is the

material that makes up genes.

DNA is the instruction manual for living things. Within the

relatively simple double helix structure, DNA holds the coded



3

information for how to make every protein a living organism

might need throughout its entire life.

Very pure DNA can be easily extracted from cells in a

research laboratory. DNA is a non-living stable molecule. The

DNA code is universal allowing it to work the same in all

living things. This is a critical fact that makes genetic

engineering possible. Genetic engineering is the directed

addition of new DNA to an organism's genetic makeup, its

genome. Once scientists understood the properties of DNA

and how it functions as genetic material, they could envision

and invent techniques for genetic engineering.

DNA extraction is necessary because genetic engineers need

to be able to work with the DNA, cut it, locate and clone a

single gene, and modify the gene before they insert it into

another organism.

DNA is composed of nucleotides bonded to a sugar-

phosphate backbone. Double stranded DNA forms a double

helix structure.

The DNA double helix coils up into compact structures called

chromosomes. Small segments of the chromosome that

encode a single protein are called genes.

Chromosomes are microscopic. There are thousands of genes

on each chromosome and hundreds of nucleotides in the

DNA sequence of each gene.

The role of DNA is to store and pass on genetic information.

The sequence of DNA subunits determines an organism's

traits.



4

DNA Structure


DNA is a macro molecule that consists of many subunits

connected together. The subunits are called nucleotides.

Each nucleotide has three parts; a sugar, a phosphate, and a

base. The sugar and phosphate molecules are linked together

in two long chains. The bases are linked to the sugar-

phosphates. Bases of one strand are bound to those of the

other strand by hydrogen bonds making what is called a base

pair. The structure of DNA is a double helix which allows it to

perform the functions of replication and information storage.

Base pairs look similar to rungs on a ladder. In fact, the DNA

structure could be described as a long ladder twisted into a

spiral.


There are only 4 nucleotides in DNA, Adenine (A), Guanine

(G), Thymine (T), and Cystosine (C). The chemical structures

of Thymine and Cytosine are smaller, while those of Adenine

and Guanine are larger. Size and structure of the specific



5

nucleotides cause Adenine and Thymine to always pair

together while Cytosine and Guanine always pair together.

Therefore the two strands of DNA are considered

complimentary.

Simple Extraction of DNA from Peas


break the plant cells open allowing the DNA to freely leave

the cell.

Why is it necessary to extract the DNA out of a cell in genetic

engineering? As mentioned above, DNA is found in the

nucleus of a cell. In order for genetic engineers to be able to

work with and transfer DNA into another organism, it must

be first taken out of the cell. Fortunately, a DNA molecule

remains somewhat stable outside of a living cell allowing

scientists the opportunity to work with and study it without

destroying it. To extract DNA, tissue samples are taken from

plants, and crushed to break open the cells.

Next, a buffered salt water solution is added into which DNA

dissolves easily. The DNA is purified by adding an organic

solution into which other molecules, such as fats and

proteins dissolve. The purified DNA solution is separated off

and the DNA is precipitated out of the solution by adding

alcohol. The DNA is now a solid string that can be spooled

out with a hook. The extracted DNA is placed into test tubes

with a weak buffer solution and can be stored almost

indefinitely.

During DNA extractions, the entire cells' DNA is extracted at

the same time. Extracted DNA has usually been sheared into

smaller pieces due to the leaf tissue grinding process. This

makes it difficult to isolate an entire chromosome in once



6

continuous strand. However, large pieces that contain several

to dozens of genes can be extracted intact with this method.

After isolating the DNA, researchers can use it for further

laboratory studies including genetic engineering.

Materials:

1. Peas, about 50 g (frozen ones are suitable, but thaw them

first)

2. SDS solution (sodium dodecyl sulfate) or washing-up liquid,

(dishwashing liquid solution) 10 cm3 (ml).

3. NaCl (Table Salt), 3 g.

4. Distilled water, 90 cm3.

5. Very cold ethanol, about 10 cm3, straight from the freezer.

6. Novozymes Neutrase® (a protease), 2–3 drops.

7. Ice with cold water.

8. Filter paper.

9. Large funnel.

Procedure:

1. Dissolve the salt in 90 cm3 of distilled water. Add the

washing-up liquid and mix gently.

2. Mash the peas using a glass rod or a spoon. Add the pea pulp

to a beaker with the salty washing-up liquid solution.

3. Stand the beaker in a water bath at 60 °C for exactly 15

minutes.

4. Cool the mixture by placing the beaker in an ice water bath

for 5 minutes, stirring frequently.

5. OPTIONAL: Pour the mixture into a blender and blend it

for no more than 5 seconds.



7

6. Filter the mixture into a second beaker. Ensure that any foam

on top of the liquid does not contaminate the filtrate.

7. OPTIONAL: Add 2–3 drops of protease to about 10 cm3 of

the pea extract in a boiling tube and mix well.

8. Very carefully pour ice cold ethanol down the side of the

boiling tube, to form a layer on top of the pea extract.

9. Leave the tube, undisturbed, for a few minutes.

10. Nucleic acids (DNA and RNA) will precipitate into the upper

(ethanol) layer


break the plant cells open allowing the DNA

to freely leave the cell.



8



9

Expected Results

A slimy white material will precipitate at the interface of the

ethanol and filtrate layers. This material consists of clumped-

together DNA strands.

Extracted soybean DNA after it has precipitated out of solution.

What's Going On?

The procedure used in this activity has the same essential

elements as more advanced laboratory DNA extraction

procedures: mechanical and thermal disruption of cells,

liberation of the DNA, and precipitation of the DNA.

In this procedure, the Pea cell walls are broken down by the

mechanical mashing and then the heating, and the detergent

dissolves the lipids in the cell membranes and nuclear

envelope. The DNA is no longer confined inside the nuclear

membranes. It is highly soluble in water because the

phosphate group of each nucleotide carries a negative charge.

However, the positively charged sodium ions from the salt in

the extraction solution are attracted to the negatively charged

phosphate groups on the DNA backbone, effectively



10

neutralizing the DNA's electric charge. This neutralization

allows the DNA molecules to aggregate with one another.

When the ethanol is added, the DNA clumps together and

precipitates at the water/ethanol interface because the DNA

is not soluble in ethanol.

Each glob of material in the precipitate will contain millions

of DNA strands clumped together, along with some of the

protein that is normally associated with DNA. Fortunately, a

DNA molecule remains somewhat stable outside of a living

cell allowing scientists the opportunity to work with and

study it without destroying it.

DNA Facts

All DNA is folded and packed into the nucleus of a human

cell. The diameter of the nucleus is about 0.005 mm or 1/500

the width of a dime.

There are 6 billion bits of information coded by DNA in each

of our nucleated cells (a bit is a measure of information).

Each human cell contains twenty-one times the information

that is found in the Encyclopedia Britannica, which is

thought to have about 280 million letters.

There are about 3 x 109 nucleotide base pairs in the human

genome (the complete set of genes in one cell). If you lay all

the DNA strands from a single human cell end to end, it

would be about 2 meters long!

Calculate how many times to the moon and back a human's

DNA would reach if it was removed from each cell and each

strand laid end-to-end. Here is the information you need:

Each cell nucleus in a human holds about 2 meters of DNA

and a typical adult human is composed of 60 trillion cells.

The distance from the earth to the moon is 380,000

kilometers.



11

Student Worksheet DNA and DNA Extraction


Name: ____________________ ID#:__________ DATE: __/4/2007

1. From where, and why, do scientists extract DNA? Give several

examples. ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

2. What is the function of DNA? ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

3. Where is DNA located?

______________________________________________________

______________________________________________________

4. Most of the bases in our DNA are (Circle one): a. coding b.non-coding 5. Below is a portion of a DNA strand. Fill in the blanks with the complementary base pairs.

A T T G C C C A A T A G G C

__ __ __ __ __ __ __ __ __ __ __ __ __ __

6. A sequence of DNA that codes for the production of a specific protein is called a: ______________________________________________________

______________________________________________________

7. State your results after observing your DNA. Do you think you have pure DNA? Why or why not? ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________



12

8. What does the salt do?

______________________________________________________

______________________________________________________

______________________________________________________

9. What does the blender do? ______________________________________________________

10. When you mix the blended cell source with the SDS (Soap),

what is happening? ______________________________________________________

______________________________________________________

______________________________________________________

11. What does the alcohol do? Why does the DNA rise to the top

after adding alcohol? ______________________________________________________

______________________________________________________

______________________________________________________

12. In the space below, draw what you saw in the test tube. Make

sure to label the solutions, the interface layer, and the DNA. ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

13. Why can’t you see the double helix? ______________________________________________________

______________________________________________________

______________________________________________________

14. What part of the cell did the DNA come from? ______________________________________________________

______________________________________________________

______________________________________________________

15. When we extracted DNA from 10 different fruits and

vegetables, we noticed that there was a lot of variation in the

amounts of DNA yielded from each. Why do some plants give

more DNA than others? ______________________________________________________

______________________________________________________

______________________________________________________



13

16. In the space below, draw a simple model of DNA. Make sure to

label the bases correctly. ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

17. Some people are concerned that we are able to manipulate the

DNA of crop plants and that it will change them into something

that they are not. Can you give some examples of the types of plant

genes that might be changed? Do you think that scientists should

proceed with this type of research? Why or why not? ______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Practical Plant Genetics

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