Bahasa
Halaman
Hukum
Struktur dan Bentuk KromosomKromosom: gen Protein ---- histon
Gen: urutan tertentu dari asam deoksiribonukleat (DNA) yang menentukan pembentukan protein, diantaranya enzim dan dapat diwariskan ---- fungsi protein??? (minimal 5)
Genom: Himpunan gen yang lengkap yang dimiliki oleh suatu organisma dalam mengendalikan seluruh proses metabolisma dalam suatu
organisme sehingga dapat hidup sempurna
Jumlah gen dalam genom berbeda untuk setiap organisma yang berlainan.
Pregnancy Loss and Chromosome Testing
for Miscarriages
Types of chromosome aberrations in human lymphocytes.
Sex Determination
Asexual organism are those for which no evidence of sexual reproduction is known.
Organism which has alternate between short periods of sexual production and prolonged period of sexual reproduction.
In diploid eukaryote organism, sexual reproduction is the only natural mechanism resulting in new members of species.
Multicellular origanisms has ► primary sexual differentiation: only gonads to produce gametes ► secondary sexual differentiation : involves other organs, such as mammary glands and external genitalia.
euchromatic regions that contain functional genes and heterochomatic region that lack genes Pseudoautosomal Region(PAR) is; - homology with region on the X chromosome , - synapse and recombine with it (X) during meiosis, - critical to the segregation of the X and Y chromosomes during male gametogenesis. Non Recombining Region of the Y (NRY) called as
male-specific region of the Y (MSY).Sex-Determined Region Y (SRY) is critical genes that
control male sexual development
In plants and animal ► unisexual, dioecious, and gonochoric are equivalent ----; individual containing only male or female reproductive organs. ► bisexual, monoecious, and hermaphroditic refer ----- individual containing both male and female reproductive organs. This later group of organisms can produce fertile gametes for both sexes. ► intersex ----- individuals of intermediate sexual differentiation, who are most often steril.
Linkage is the condition where two or more nonallelic genes tend to be inherited together. Linked genes have their loci along the same chromosome; they do not assort independently but can be separated by crossing over.
Linkage and Crossing Over
Sex-linked Genes (X-linked genes)
Sex Chromosom in Human and Drosophila: X and Y
- Sex chromosome X : in female- Sex chromosome Y : in male * region of pairing homology with the X chromosome (synapse and segregate during meiosis, PAR) * male-specific region of the Y (MSY) considered to be relatively inert genetically.
X-Linked in Human
genes present on the X chromosome exhibit unique patterns of inheritance in comparison with autosomal genes.
A. Hemofilia: - Suffers from bleeding because of slow clotting blood. The recessive gene (h), links to the sex chromosome-X - All male offspring from a mother with hemophilia will suffer from hemophilia because they inherit one sex chromosome-X from their mother. - female offspring are not necessarily to be hemophilia because the allele may be heterozygous Hh, except if the father is also hemophilia.
B. Collor Blindness The allele for color blindness c (recessive) is linked to the sex
chromosome-X Most of the sufferer of color blindness is male.
Condition Characteristics
Color blindness type:
a. deutan type Insensitivity to green light
b. protan type Insensitivity to red light
Fabry disease Deficiency of galactosidase A: Heart and kidney defects, early death.
G-6-PD deficiency Deficiency of glucose-6-phosphate dehydrogenase, severe anemic reaction following intake of primaquines in drugs and certain foods, including fava beans.
Hemophilia A Classical form of clothing deficiency, absence of clothing factor VIII
Hemophilia B Christmas disease, absence of clothing factor IX
Hunter Syndrome Mucopolarysaccharide storage disease resulting from iduronate sulfatase enzyme deficiency, short stature, clawlike fingers, coarse facial features, slow mental deterioration, and deafness.
Ichtyosis Deficiency of steroid sulfatase enzyme, scaly dry skin, particularly on extremities.
Lesch-Nyhan Syndrom
Deficiency of hypoxanthine-guanine phosphorybosyl transferase enxyme (HGPRT) leading to motor and mental retardation, self mutilation, and early death.
Duchene Muscular Dysstrophy
Progressive, life-shortening disorder characterized by muscle degeneration and weakness, sometimes associated with mental retardation, absence of protein dystrophin.
X-linked in Drosophila Thomas H MorganWhite eyes (mutant, recessive) vs. red eye (wild-type, dominant)
mutant wild-type
Crossing Over
Linked genes have their loci along the same chromosome; they do not assort independently but can be separated by crossing over.
Crossing over is the exchange of chromosomal material (parts of chromosomal arms) between homolog chromosomes by breakage and reunion.
The exchange of material between nonsister chromatids during meiosis is the basis of genetic recombination.
During the first meiotic prophase, when homolog are paired or synapsed, a reciprocal exchange of chromosome segments can take place. This crossing over result in the reshuffling, or recombination, of the alleles between homolog and always occurs during the tetrad stage.
17.3-plant_cell_division.mov
Linkage Ratio
Drosophilabw+ = red eyes, wild type, dominantbw = brown eyes, mutant, recessivehv+ = thin vein, wild type, dominanthv = heavy vein, mutant, recessive
Crossover Linkage
y = yellow body, mutant, recessivey+ = grey body, wild type, dominantw = white eyes, mutant, recessivew+ = red eyes, wild type, d ominantm = miniature wing, mutant, recessivem+ = normal wing, mutant, dominant
Phenotype progeny F21) yellow - white 0,5 %2) white - miniature 34,5 % 3) yellow - miniature 35,4 %
0,5 34,5
35,4
y w m
Single Crossover
Crossover can occur between two sister or non-sister chromatids and between two-genes that arelinked or not linked to each other.● between two sister chromatids or between not linked
genes ---- No recombinant gamete produced● between two non-sister chromatids and linked genes ----
Recombinant gamete produced. The ratio of the recombinant chromosome and
parental chromosomes produced = 1 : 1.
50% of the potential gametes formed are recombinant
Multiple Crossover
In one tetrad are more than 2 crossovers (CO). Frequency CO among linked genes is highly
affected by the distance among genes. For example: recombinant gametes of single crossover (SCO)
between gene A and gene B = 20% between gene B and gene C = 30% Therefore, double crossover (DCO) between gene A and gene C is (0,20) x (0,30) = 6% (0,06). So the probability DCO < SCO
Pemetaan kromosom
2 hipotesis yang diajukan morgan tentang pindah silang.1. Gen-gen dalam suatu organisme tersusun secara linier sepanjang kromosom.2. Frekuensi turunan yang menunjukkan fenotip rekombinan/pindah silang dapat digunakan untuk menentukan letak relatif gen-gen terpaut di dalam satu kromosom.
Contoh: alel sifat menurun (inheritance) bentuk dan warna sayap yang diamati pada persilangan Drosophila adalah sebagai berikut: B = sayap kelabu V = sayap panjangb = sayap hitam v = sayap kisut
Persilangan drosophila dengan sifat sifat :Betina JantanSayap kelabu panjang x Sayap hitam kisut (BBVV) (bbvv)
F1 : Semua betina bersayap hitam dan kisut (bbvv) Semua jantan bersayap kelabu panjang (B-V-)
Fenotip warna dan Bentuk Sayap Genotip Jumlah
(ekor) Tipe
kelabu dan panjang B-V- 822 parentalkelabu dan kisut B-vv 130 rekombinan
hitam dan panjang bbV- 161 rekombinanhitam dan kisut bbvv 652 parental
Jumlah 1765
F2 : hasil persilangan antara turunan F1
komposisi turunan(filial) F2
Sturtevant dan pemetaan kromosom
Temuan dan hipotesis morgan digunakan Sturtevant untuk membuat 2 hipotesis dalam menentukan jarak antar gen. 1. jarak antara gen-gen yang terpaut dalam satu kromosom.2. Distribusi linier gen sepanjang kromosom dapat digunakan sebagai dasar untuk menentukan peta
kromosom
Kesimpulan: * Frekuensi pindah silang gen kecil ---- jarak antar gen-gen
terpaut dekat * Frekuensi pindah silang gen besar ---- jarak antar gen-gen
terpaut jauh
Frekuensi pindah silang (PS) = nilai pindah silang (NPS) NPS = ∑ turunan tipe rekombinan
∑ turunan
Jadi berdasarkan data hasil persilangan di atas maka : NPS = 130 + 161/ 1765 = 16.15% Jarak antara alel untuk bentuk dan warna sayap dalam
kromosom adalah16.5 unit
Tiga titik dalam pemetaan kromosom Drosophila
1. Pindah silang antar gen-gen yang berdampingan baru bisa berlangsung bila jarak antara gen tersebut > 5 unit peta 2. Bila jarak antara 2 gen yang berdekatan sangat besar, misal 17 unit, maka diantara dua gen tersebut dapat terjadi multipel pindah silang.
Multiple pindah silang selalu memberikan hasil yang berbeda padaturunannya karena selalu terbentuk turunan tipe rekombinan bila terjadidiantara lebih dari 2 gen yang berdampingan (lebih dari 2 titik). Jadi minimal harus terjadi pada 3 titik peta (3 point mapping) dengan syarat-syarat sbb. 1. Genotip organisme harus heterozygot pada seluruh lokus yang
diamati 2. Harus dapat melakukan persilangan antara organisme-organisme untuk menghasilkan jumlah keturunan yang banyak
Contoh : dilakukan persilangan Drosiphila untuk mengamati sifat warna badan serta bentuk sayap dan mata dengan alel-alel sebagai berikut:
y= badan kuning, mutan, resesif y+ = badan kelabu, wild type, dominan ec = mata kasar, mutan, resesif ec+ = mata normal, wild type, resesif ct = sayap pendek, mutan, resesif ct+ = sayap normal, wild type, dominan
Parental: Betina Jantan+ + + x y ec ct+ + + y ec ct
F1 : semua turunan berbadan kuning, bermata normal, bersayapnormal
+ + + y ec ct
F2 : Dari hasil persilangan antara turunan F1 diperoleh hasil komposisi turunan (filial) sebagai berikut :
Genotip Jumlah(ekor) Tipe Pindah Silang
+ + + 1080 parentaly ec ct 1071 parentaly + + 78 pindah silang tunggal
+ ec ct 66 pindah silang tunggaly ec + 282 pindah silang tunggal+ + ct 293 pindah silang tunggaly + ct 4 pindah silang tunggal
+ ec + 6 pindah silang tunggalJumlah 2280
Penentuan urutan gen dalam kromosom
Urutan susunan gen dalam kromosom di atas akan ditentukanberdasarkan jaraknya Dengan cara perhitungan sbb.
NPS ganda antara y – ec = 78 + 66 + 4 + 6/2280 x 100% = 5,4% NPS ganda antara ec – ct = 282 + 293 + 4 +6/2280 x 100% = 20,3% NPS ganda antara y – ct = 78 + 66 + 282 + 293/2280 x 100% = 24,9%
Jadi urutan dan jarak antar gen yang mungkin adalah
y------ --ec-------------------------ct 5,4 20,3 y----------------24,9---------------ct
Interferensi dan koinsidansi (I)
Interferensi adalah pengurangan jumlah pindah silang yangterjadi diantara gen-gen yang terletak bersisian satu sama lain pada suatu kromosom. Besarnya nilai I ditentukan dengan rumus:
I = 1- C, C = koofisien koinsiden
C = PS yang terlihat (DCOo) PS yang tidak terlihat (DCOe)
DCOe = (NPS y-ec)(NPS ec-ct) = 0,054 x 0,203 = 0,011 = 1,1% DCOo = 4 +6/2280 = 0,034 = 0,34% C = 0,34/1.1 = 0,31%
Jadi hanya 0,31 % pindah silang ganda yang diharapkanterjadi antara gen y – ct.
Dari perhitungan diatas maka nilai I yang diperoleh adalah
I = 1 – 0,31 = 0,69
Bila I = 0, tidak terjadi multiple pindah silang (DCO)
I = 1, DCOe > DCOoI ≥ 0, DCOe > DCOoI ≤ 0, DCOe < DCOo
Copyright © 2022 FDOKUMEN
