In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A recessive lethal allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female?
A) 2:1 male to female
B) 1:2 male to female
C) 1:1 male to female
D) 3:1 male to female

Question

Quizplus · Accepted Answer

The male is heterozygous (ZlZ) and the female is normal (ZW). The possible offspring are ZlZ (lethal, dies), ZZ (male), ZlW (female), and ZW (female). The viable offspring are 1 male (ZZ) and 2 females (ZlW, ZW), resulting in a 2:1 male to female ratio.

In Birds, Sex Is Determined by a ZW Chromosome Scheme