in chickens four comb phenotypes occur (single comb, walnut comb, pea comb and r
ID: 132222 • Letter: I
Question
in chickens four comb phenotypes occur (single comb, walnut comb, pea comb and rose comb), Comb type is determined by two genes acting together (the A gene and the B gene)each of these genes has two alleles (a dominant allel and a recessive one) the relationship between genotype and phenotype is as follows
genotype phenotype
aabb single comb
aaB_ pea comb
A_bb rose comb
A_B_ walnut comb
a. what comb types in what porportions will appear in the F1 and in the F2 if a single combed bird is crossed with a walnut combed bird (if the walnut combed bird is homozygous for both genes)
b. if a walnut combed bird is crossed with a rose combed bird and the offspring are 3/8 rose comb, 3/8 walnut comb, 1/8 pea comb and 1/8 single comb, what are most likely genotypes of the parents.
c. if a walnut combed is crossed with a rose combed bird and the offspring are all walnut comb what are the mostly likely genotypes of the parents?
d. how many different genotypes will produce the walnut comb phenotype?
Explanation / Answer
A) If single combed bird (aabb) is crossed with walnut combed bird (AABB), the F1 will be all walnut combed with the genotype AaBb. In the F2 generation, walnut combed, pea combed, rose combed and single combed offsprings are produced in the ratio of 9:3:3:1.
B) If Aabb (rose combed) and walnut combed (AaBb) are crossed, offsprings obtained are 3/8 rose comb, 3/8 walnut comb, 1/8 pea comb and 1/8 single comb.
C) If a walnut combed is crossed with a rose combed bird, all the offsprings are walnut combed. So, the possible genotypes of patents are,
AABB x AAbb and AABB x Aabb
D) Walnut comb phenotype is produced by AABB, AaBB, AaBb genotypes.
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