In chickens, males have two Z sex chromosomes (ZZ) and females have one Z and one W sex chromosome (ZW). The mechanism for inheritance of the sex chromosomes is exactly the same as for X and Y sex chromosomes in other species. In chickens the character of ‘barred’ or striped feathers is Zchromosome linked. The barred feather allele ZB is dominant to the nonbarred feather allele Zb. Write down the genotype that would result in a nonbarred male and a barred female and explain why these are the only genotypes that could result in these phenotypes.

To determine the genotype that would result in a nonbarred male (ZbZb) and a barred female (ZBZW), let's break down the possible combinations of sex chromosomes and alleles.

In this scenario, the male has two Z sex chromosomes (ZZ) and needs to be nonbarred (ZbZb). Since the nonbarred feather allele is Zb and it is recessive to the barred feather allele ZB, the male must inherit the nonbarred allele from both parents. Therefore, the male genotype is ZbZb.

On the other hand, the female has one Z and one W sex chromosome (ZW) and needs to be barred (ZBZW). As the barred feather allele is dominant, the female can inherit it from a single parent. Since the nonbarred allele is recessive, the female will express the barred phenotype if she receives the ZB allele from either the father or the mother. Thus, the female genotype is ZBZW.

These are the only possible genotypes that could result in the given phenotypes because the barred feather allele is dominant to the nonbarred feather allele. Therefore, a male must have two copies of the nonbarred allele (Zb) to exhibit the nonbarred phenotype, while a female can exhibit the barred phenotype by inheriting just one copy of the barred allele (ZB).