Chapter 14, Problem 10TYPSS

The smooth feathers on the back of the neck in pigeons can be reversed by a mutation to produce a “crested” appearance in which feathers form a distinctive spike at the back of the head. A pigeon breeder examined offspring produced by a single pair of non-crested birds and recorded the following: 22 non-crested and 7 crested. She then made a series of crosses using offspring from the first cross. When she crossed two of the crested birds, all 20 of the offspring were crested. When she crossed a non-crested bird with a crested bird, 7 offspring were non-crested and 6 were crested.

• For these three crosses, provide genotypes for parents and offspring that are consistent with these results.

• Which allele is dominant?