In birds the male has two identical sex chromosomes designated ZZ, whereas the f

ID: 53339 • Letter: I

Question

In birds the male has two identical sex chromosomes designated ZZ, whereas the female has one Z as well as a nearly blank chromosome, designated W (females are ZW). In parakeets two genes control feather color. The presence of the dominant Y allele at the first gene results in the production of a yellow pigment. The dominant B allele at the second gene controls melanin production. When dominant alleles are present for both genes, the feathers are green. If a dominant allele is only present for the Y gene, the feathers are yellow. If a dominant allele is only present for the B gene, the feathers are blue. If dominant alleles are not present at either gene, the feathers have no color (albino). A green male parakeet (P1) was crossed with an albino female parakeet (P2) producing all green F1 progeny. When F1 males and females were allowed to mate they produced F2 progeny with phenotypes in the following ratios:

3/8 green males
3/16 green females
1/8 yellow males
1/16 yellow females
3/16 blue females
1/16 albino females

What is the genotype of the P1 green male parakeet?
A) YYBB
B) YyBB
C) YYBb
D) YyBb

Which, if any, of the genes controlling feather color in parakeets is Z-linked?
A) Y is Z-linked, B is autosomal
B) B is Z-linked, Y is autosomal
C) Both Y and B are Z-linked
D) Both Y and B are autosomal

Explanation / Answer

What is the genotype of the P1 green male parakeet?
A) YYBB

Which, if any, of the genes controlling feather colour in parakeets, is Z-linked?

A) Y is Z-linked, B is autosomal

Explanation:

Y allele-Yellow pigment

B allele- controls melanin production

Y-B-= Green

Y-bb=Yellow

yyB-=Blue

yybb=Albino

Genotype

Phenotype

YYbb and Yybb

Yellow

yyBB and yyBb

Blue

YYBB and YyBb

Green

Yybb

Albino

P: green male YY BB X albino female yW bb has resulted in all green progeny

F1: 1/2 green males Yy Bb, 1/2 green females YW Bb, so half of are the males and half of are the females

F2: 6/16 green males Y- B -

2/16 yellow males Y - bb

3/16 green females YW B-

1/16 yellow females YW bb

3/16 blue females yW B-

1/16 albino females yybb

By observing the F2 males, we can say that the Y allele is located on Z, as all males are getting Y form their mother, but at the same time they are getting B always, this shows that mother is heterozygous for B (Bb) and this shows that this allele is located on autosomal chromosome.