In the Jubjub bird, the gene G controls feather color. The dominant allele G giv
ID: 302413 • Letter: I
Question
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 6Explanation / Answer
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.
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