Question

In chickens the females are heterogametic, ZW, and the males are homogametic, ZZ. Most sex-linked genes are only carried on the Z chromosome. Congenital baldness is caused by a recessive sex-linked allele. If a bald male is crossed to a normal female, what would be the expected results in the offspring?

a. All the offspring will be bald regardless of sexual phenotype.
b. All the males will be normal and all the females will be bald.
c. Half the offspring will be bald and half will be normal regardless of sexual phenotype.
d. All the offspring will be normal regardless of sexual phenotype.
e. All the females will be normal and all the males will be bald.

Answer 1

In the case of chickens, with sex-linked congenital baldness, a cross between a bald male and a normal female will result in all male offspring being normal and all female offspring being bald.

Step-by-step explanation:

In chickens, which exhibit a ZW sex-determination system, females are heterogametic ZW, and males are homozygotic ZZ. For the case of sex-linked congenital baldness caused by a recessive allele found only on the Z chromosome, if a bald male chicken (ZZ, with at least one Z having the baldness allele) is crossed with a normal female (ZW, without the baldness allele), the expected results in the offspring will be that all males (ZZ) will be normal, as they inherit a normal Z from their mother and a bald Z from their father, while all females (ZW) will be bald, as they inherit the baldness Z from their father and a W from their mother, which does not carry the allele for normal feathering.

Therefore, the correct answer to the given question is:

• b. All the males will be normal and all the females will be bald.