In: Biology
In the Jubjub bird, the gene G controls feather color. The dominant allele G gives rise to black pigmentation, and the recessive allele g gives rise to a pale gray color when homozyous. The gene D regulates size. The dominant allele D gives rise to giant jubjubs with wingspans over 5 meters, and dwarfism, with wingspans averaging 3 meters, is recessive. The ability to talk is also recessive. The dominant allele of the T locus results in mute birds. A single female jubjub bird can lay a clutch of over 900 eggs. A fully heterozygous female was mated with a dwarf, gray male who could talk. The offspring were counted. Please indicate whether any or all of these genes assort independently of one another. Map any linked loci.
Color | Adult Size | Speech | Number of Offspring |
Black | Giant | Mute | 5 |
Black | Giant | talking | 17 |
Black | dwarf | Mute | 0 |
Black | dwarf | talking | 361 |
gray | Giant | Mute | 379 |
gray | Giant | talking | 0 |
gray | dwarf | Mute | 14 |
gray | dwarf | talking | 6 |
Answer:
All genes are present in the same chromosome and they are not at all assorted independently.
Gene map:
G----------1.22 mu--------T-----------3.44 mu--------------D
Explanation:
Based on the information, the cross is test cross. If the genes are not linked and they are assorted independently, the trihybrid testcross ratio is “1:1:1:1:1:1:1:1”
But the number of offspring produced is not in the ratio mentioned above. Therefore the genes are linked.
Hint: Always recombinant genotypes are smaller than the non-recombinant genotypes.
Hence, the parental (non-recombinant) genotypes is Gdt/gDT
Color |
Adult Size |
Speech |
Number of Offspring |
Genotype |
Black |
Giant |
Mute |
5 |
GDT |
Black |
Giant |
talking |
17 |
GDt |
Black |
Dwarf |
Mute |
0 |
GdT |
Black |
Dwarf |
Talking |
361 |
Gdt |
gray |
Giant |
Mute |
379 |
gDT |
gray |
Giant |
Talking |
0 |
gDt |
gray |
Dwarf |
Mute |
14 |
gdT |
gray |
Dwarf |
Talking |
6 |
gdt |
1).
If single crossover occurs between G&d..
Normal combination: Gd/gD
After crossover: GD/gd
GD progeny= 5+17=22
gd progeny = 6+14=20
Total this progeny = 42
The recombination frequency between G&d = (number of recombinants/Total progeny) 100
RF = (42/900)100 = 4.67%
2).
If single crossover occurs between d & t..
Normal combination: dt/DT
After crossover: dT/Dt
dT progeny= 14+0=14
Dt progeny = 17+0=17
Total this progeny = 31
The recombination frequency between d&t = (number of recombinants/Total progeny) 100
RF = (31/900)100 = 3.44%
3).
If single crossover occurs between G&t
Normal combination: Gt/gT
After crossover: GT/gt
GT progeny= 5+0=5
gt progeny = 6+0=6
Total this progeny = 11
The recombination frequency between G&t = (number of recombinants/Total progeny) 100
RF = (11/900)100 = 1.22%
Recombination frequency (%) = Distance between the genes (mu)
G----------1.22 mu--------T-----------3.44 mu--------------D
All genes are present in the same chromosome and they are not at all assorted independently.