One trait that chicken breeders wished to produce was barred feathers, which causes the feathers to look like they have a striped pattern (see image below). The allele for barred feathers is dominant and it is located on the sex chromosome, so the trait is considered to be sex linked. Chickens are a bit different from humans in that the male carries two of the same chromosomes to determine gender (ZZ), and the female carries one of each type of sex chromosome (ZW). Therefore, males carry two alleles for this trait and females carry only one. A male chicken that is not barred and a female that is barred are crossed. What percentage of the females will be barred?

0% of the females will be barred. This means that none of the females will be barred.

Explanation: From the information given, barred feathers is sex linked and the allele for barred feathers is dominant. Males are usually carriers because they have have two of the same type of chromosome (ZZ), their two chromosomes have to be affected for them to become barred. Females are usually sufferers because they have only Z chromosome, which once affected will manifest as barred feathers.

Let ZB represent the allele for barred feathers, a male that is not barred has a genotype of ZZ and a female that is barred will have a genotype of ZBW. A cross between two of them will produce 2 males that are heterozygous for barred feathers (ZBZ) and 2 females that have normal feathers (ZW).

See attached punnet square for more information.