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.

Question

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.

Answer 1

To determine the genotype that would result in a nonbarred male (with two Z sex chromosomes) and a barred female (with one Z and one W sex chromosome), we first need to understand the inheritance pattern of the barred feather allele (ZB) and the nonbarred feather allele (Zb).

In chickens, since males have two Z sex chromosomes (ZZ), they inherit one Z chromosome from each parent. Females, on the other hand, have one Z and one W sex chromosome (ZW), inheriting the Z chromosome from the father and the W chromosome from the mother.

The fact that the barred feather allele (ZB) is dominant over the nonbarred feather allele (Zb) means that if an individual has at least one copy of the ZB allele, the barred phenotype will be expressed. The nonbarred phenotype will only be expressed in individuals who have two copies of the recessive Zb allele.

Now, let's consider the possible genotypes that could result in a nonbarred male and a barred female.

For a nonbarred male, he must have two copies of the recessive nonbarred feather allele (Zb). Since males have two Z chromosomes (ZZ), and he must be nonbarred, both Z chromosomes must carry the nonbarred feather allele (Zb). Therefore, the genotype of the nonbarred male would be ZbZb.

For a barred female, she must carry at least one copy of the dominant barred feather allele (ZB). Females have two different sex chromosomes (ZW) and only inherit one Z chromosome from their father. To express the barred phenotype, she only needs one copy of the ZB allele. However, since there are no restrictions regarding the W allele, the other chromosome can carry any allele for feather barring. Therefore, the genotype of the barred female could be either ZBZB or ZBZb.

These are the only possible genotypes that could result in the given phenotypes of a nonbarred male and a barred female.