A recessive gene for red -green color blindness is located on the X chromosome in humans. Assume that a woman with normal vision (her father is color -blind) marries a color -blind male. What is the likelihood that this couple's first son will be color -blind?
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) 1:2 male to female B) 4:1 male to female C) 1:1 male to female D) 2:1 male to female E) 3:1 male to female
A) scheme based on single translocations in the X chromosome B) scheme based on F plasmids inserted into the FMR -1 gene C) XX/XO scheme D) XO/YY scheme E) hermaphroditic scheme