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 femaleb) 1: 2 male to femalec) 1: 1 male to femaled) 3: 1 male to female