Question

The sex of birds, some insects, and other organisms is determined by a ZW chromosomal

arrangement in which the males have like sex chromosomes (ZZ) and females are ZW (similar to
XY in humans). Assume that a recessive lethal allele on the Z chromosome causes death of an
embryo in birds. What sex ratio would result in the offspring if a cross were made between a male
heterozygous for the lethal allele and a normal female?
A) 4:1 male to female
B) 1:1 male to female
C) 3:1 male to female
D) 2:1 male to female
E) 1:2 male to female

Answer 1

The cross between a male heterozygous for the lethal allele and a normal female in birds with a ZW chromosomal arrangement would result in a 2:1 male to female sex ratio in the offspring.

Step-by-step explanation:

The cross between a male heterozygous for the lethal allele and a normal female in birds with a ZW chromosomal arrangement would result in a 2:1 male to female sex ratio in the offspring.

This is because the male can pass on either a normal Z allele or a lethal Z allele, while the female can only pass on a normal W allele.

Therefore, there would be twice as many males with the normal Z allele and one fewer female with the normal W allele in the offspring.