Getting to Know Fly Lab

Week 6

Getting to Know Fly Lab

Performing Crosses

Professor:

BIOS-135

Johann Gregor Mendel (1822-1884)

Father of Genetics

“Gregor Mendel, through his work on pea plants, discovered

the fundamental laws of inheritance. He deduced that genes

come in pairs and are inherited as distinct units, one from

each parent. Mendel tracked the segregation of parental

genes and their appearance in the offspring as dominant or

recessive traits. He recognized the mathematical patterns of

inheritance from one generation to the next. Mendel's Laws

of Heredity are usually stated as:

1) The Law of Segregation: Each inherited trait is defined

by a gene pair. Parental genes are randomly separated to the

sex cells so that sex cells contain only one gene of the

pair. Offspring therefore inherit one genetic allele from

each parent when sex cells unite in fertilization.

2) The Law of Independent Assortment: Genes for different

traits are sorted separately from one another so that the

inheritance of one trait is not dependent on the inheritance

of another.

3) The Law of Dominance: An organism with alternate forms of

a gene will express the form that is dominant.

The genetic experiments Mendel did with pea plants took him

eight years (1856-1863) and he published his results in

1865. During this time, Mendel grew over 10,000 pea plants,

keeping track of progeny number and type. Mendel's work and

his Laws of Inheritance were not appreciated in his time. It

wasn't until 1900, after the rediscovery of his Laws, that

his experimental results were understood.” (Center, 2011).

Fly lab Notes for DeVry Biology

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Results of Cross #1

Parents

(Female: +) x (Male: +)

Offspring

Phenotype Number Proportion Ratio

Female: + 5043 0.5031

1.013

Male: + 4980 0.4969

1.000

Total 10023

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Results of Cross #1

Parents


Offspring


Female: + 5043 0.5031

1.013

Male: + 4980 0.4969

1.000

Total 10023

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Results of Cross #1

Parents


Offspring


Female: + 5043 0.5031

1.013

Male: + 4980 0.4969

1.000

Total 10023

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Results of Cross #2

Parents

(Female: +) x (Male: SE)

Offspring


Female: + 4945 0.4960

1.000

Male: + 5025 0.5040

1.016

Total 9970

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Results of Cross #2

Parents


Offspring


Female: + 4945 0.4960

1.000

Male: + 5025 0.5040

1.016

Total 9970

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Results of Cross #3

Parents

(Female: VG) x (Male: VG)

Offspring


Female: VG 5043 0.5022

1.009

Male: VG 4999 0.4978

1.000

Total 10042

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Results of Cross #4

Parents

(Female: E) x (Male: E)

Offspring


Female: E 5023 0.4954

1.000

Male: E 5117 0.5046

1.019

Total 10140

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Results of Cross #5

Parents

(Female: DP) x (Male: DP)

Offspring


Female: DP 5050 0.5030

1.012

Male: DP 4990 0.4970

1.000

Total 10040

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Results of Cross #6

Parents

(Female: BW) x (Male: BW)

Offspring


Female: BW 5015 0.5002

1.001

Male: BW 5011 0.4998

1.000

Total 10026

The first cross between a WT female and a WT male are shown

in

Table 1:

Fly lab Notes for DeVry Biology

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Results of Cross #1

Parents


Offspring


Female: + 5043 0.5031

1.013

Male: + 4980 0.4969

1.000

Total 10023

There are two types of chromosomes and this type identifies

the sex of the organism. We have the x and the y. in most

plants and animals, we see them are x and y only but in

humans, we call it the male and female and to most mammals

as well. During the combination of chromosomes or what we

call meiosis there is a segregation of the egg and sperm

cells then they will be paired. This normally happens during

mating. The pair that forms determines the gender of the

offspring. For female offspring, the pair is XX while XY

represents a male offspring (Gilbert, 2000; Griffiths, et

al., 2000).

One organism we will look at is the fruit flies or known as

Drosophila melanogaster. The offspring of a fruit fly is also

being determined by and XX and XY combination. Two X

chromosomes means it got a female offspring while a single x

chromosome represents a male one. In the mating process, the

chance of getting an xx or xy pair is 1:1 all the time 1

(Gilbert, 2000; Griffiths, et al., 2000).

The predicted value we have above is supported by the

information we have in Table 1. It shows in table 1 the

ration of xx and xy pairing which is 1:1.

Monohybrid Cross

Using Mendel’s law of segregation, we will see a monohybrid

cross. In this law, we uses alleles that are segregated.

Using one allele at a time, it is randomly transferred to

the gamete (Khanna, 2010).

Khanna posits that an organism’s phenotype appearance will

be lead over by the alleles’ dominant appearance. This is

through heterozygote. Looking at the phenotype of the F1 and

F2 generation, we can determine the dominant and recessive

alleles. The traits would be of the alleles since it is more

dominant. For the inheritance, Punnet square can be used to

predict its ratio. In this sample, we will use D for

dominant and d for recessive ones. If the mating happens

between a DD and dd, the offspring will be Dd on the first

generation. If there will be cross breeding soon, the F1

generation will yield a phenotype ratio of 3:1.

Check the table below for further samples.

Table 2. Punnet square of F1 generation

d d

D Dd Dd

D Dd Dd

Table 3. Punnet square of F2 generation

D d

D DD Dd

d Dd dd

Wild Type (WT) vs Sepia Eyes (SE)

The results for the F1 and F2 generation for WT and SE cross

are shown in Table 4.

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Results of Cross #2

Parents


Offspring


Female: + 4945 0.4960

1.000

Male: + 5025 0.5040

1.016

Total 9970

Results of Cross #3

Parents

(Female: VG) x (Male: VG)

Offspring


Female: VG 5043 0.5022

1.009

Male: VG 4999 0.4978

1.000

Total 10042

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In table 4, it shows that the SE or sepia eyes is recessive

and is not observed in F2 at all hence the ration after

mating id 1:3. This concludes the hypothesis we have earlier

about dominant and recessive phenotypes.

Wild Type (WT) vs VG (Vestigial Wing)

The results for the F1 and F2 generation for WT and VG cross


Table 5. Results for the F1 and F2 generation for WT and VG

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Results of Cross #4

Parents

(Female: E) x (Male: E)

Offspring


Female: E 5023 0.4954

1.000

Male: E 5117 0.5046

1.019

Total 10140

Results of Cross #5

Parents

(Female: DP) x (Male: DP)

Offspring


Female: DP 5050 0.5030

1.012

Male: DP 4990 0.4970

1.000

Total 10040

In this table, the VG or vestigial wing is recessive and is

also not seen in F1. This gives as a ratio of 1:3 as well.

It coincides with the fact that recessive type might not

show in the first generation.

Wild Type (WT) vs Ebony Body (E)

The results for the F1 and F2 generation for WT and E cross


Results of Cross #6

Parents

(Female: BW) x (Male: BW)

Offspring


Female: BW 5015 0.5002

1.001

Male: BW 5011 0.4998

1.000

Total 10026

Results of Cross #7 (F2, WT vs E)

Ignoring Sex

Parents


Offspring


+ 7601 0.7532 3.051

E 2491 0.2468 1.000

Total 10092

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In this table, table 6, the E or ebony body is recessive and

is also not seen in F1. This gives as a ratio of 1:3 as

well. It coincides with the fact that recessive type might

not show in the first generation.

Wild Type (WT) vs Dumpy Wing (DP)

The results for the F1 and F2 generation for WT and DP cross


Results of Cross #8 (F1, WT vs DP)

Ignoring Sex

Parents

(Female: +) x (Male: DP)

Offspring


+ 10010 1.0000 1.000

Total 10010

Results of Cross #9 (F2, WT vs DP)

Ignoring Sex

Parents


Offspring


+ 7454 0.7565 3.107

DP 2399 0.2435 1.000

Total 9853

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In this table, table 7, the E or ebony body is recessive and

is also not seen in F1. This gives as a ratio of 1:3 as


not show in the first generation. Earlier predictions are

true on this part.

Wild Type (WT) vs Brown Eye (BW)

The results for the F1 and F2 generation for WT and BW cross


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Results of Cross #10 (F1, WT vs BW)

Ignoring Sex

Parents

(Female: +) x (Male: BW)

Offspring


+ 10074 1.0000 1.000

Total 10074

Results of Cross #11 (F2, WT vs BW)

Ignoring Sex

Parents


Offspring


+ 7420 0.7503 3.005

BW 2469 0.2497 1.000

Total 9889

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In this table, table 8, the BW or brown eyes is recessive

and is also not seen in F1. This gives as a ratio of 1:3 as


not show in the first generation. Earlier predictions are

true on this part.

Dihybrid Cross

As the word implies, it means there are two traits being

crossed reference here. Using law of independent assortment,

the chance of a trait to emerge depends on the other’s

traits (Khanna, 2010).

In a dihybrid, the heterozygotes ratio is 1 on the F1

generation. If there will be a cross breeding, the ratio

would be 9:3:3:1at F1 (Khanna, 2010). Using Punnet square,

you can determine the expected phenotypes in dihybrid cross.

Say we have two real parents in alleles that are alleles

DDEE and ddee, we will show you the possible F1 and F2

generation in the table below.

Table 9. F1 generation of dihybrid cross DDEE and ddee

de de de de

DE DdE

e

DdE

e

DdE

e

DdE

e

DE DdE

e

DdE

e

DdE

e

DdE

e

DE DdE

e

DdE

e

DdE

e

DdE

e

DE DdE

e

DdE

e

DdE

e

DdE

e

Table 10. F2 generation of dihybrid cross DdEe and DdEe

DE De DE de

DE DDEE DdEe DdEe DdEe

De ddee DDee DdEe Ddee

DE ddee DdEe ddEE ddEe

de DdEe Ddee ddEe ddee

Legend:

Both dominant phenotype (yellow): 9

D dominant and e recessive phenotype (green): 3

D recessive and E dominant phenotype (turquoise): 3

Both recessive phenotype (pink): 1

Wild Type (WT) vs Sepia Eye (SE), Dumpy Wing (DP)

The results for the F1 and F2 generation for WT and SE, DP

cross are shown in Table 11.

Table 11. Results for the F1 and F2 generation for WT and

SE, DP

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Results of Cross #14 (F1, WT vs SE, DP)

Ignoring Sex

Parents

(Female: +) x (Male: SE; DP)

Offspring


+ 10074 1.0000 1.000

Total 10074

Results of Cross #15 (F1, WT vs SE, DP)

Ignoring Sex

Parents


Offspring


+ 5632 0.5599 9.026

SE 1963 0.1951 3.146

DP 1840 0.1829 2.949

SE; DP 624 0.0620 1.000

Total 10059

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Table 11 shows that in F1 generation, there is a ratio of 1

for the F1 and a ratio of 9:3:3:1 for the F2 generation.

This reflects our prediction above.

REFERENCES

Gilbert, S. F. (2000). Developmental Biology, 6th ed.

Sunderland: Sinauer Associates.

Griffiths, A. J. F., J. H. Miller, D. T. Suzuki, R. C.

Lewontin, and W. M. Gelbart. (2000). an Introduction to

Genetic Analysis, 7th Ed. New York: W. H. Freeman.

Khanna, P. (2010). Essentials of Genetics. New Delhi: I. K.

International Publishing.

Center, D. L. (2011). Children resemble their parents. Retrieved

from dnaftb: http://www.dnaftb.org/1/bio.html

Getting to Know Fly Lab

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