Question

20. (6) A black feathered cow bird hatches a chick that is white due to a mutation in the gene that makes the black pigment. This white bird manages to mate with a wild type black bird. The offspring are iridescent grey. Explain briefly how this mating resulted in the new color of cowbird. If the grey cowbird mates with a black cowbird, what will be the color of the offspring? Write the alleles assumed in each, and the result of the cross. Use B and b for the alleles.

Answer 1

Let us assume , gene for the color of feather as B,and the allele are B(dominant) and b (recessive)

here, the chick born to the blackbird is white due to some mutation in the gene B. .and the allele responsible for the black color get mutated. so the chick should be heterozygous (Bb) in which B allele is mutated.

when this chick(Bb) is mated with a black bird(BB) we get a GREY colored bird (Bb) due to co-dominance.( both black and white get expressed producing a intermediate color grey)

when this grey colored bird(Bb) is mated with the black bird(BB)

	B	B
B	BB	BB
b	Bb	Bb

the progeny will be back and grey in 1:1 ratio