Joe is color blind. both his mother and his father have normal vision, but his mother's father (joe's maternal grandfather) is c
olor blind. all joe's other grandparents have normal color vision. joe has three sisters—patty, betsy, and lora—all with normal color vision. joe's oldest sister, patty, is married to a man with normal color vision; they have two children, a 9-year-old color-blind boy and a 4-year-old girl with normal color vision. what is the most likely mode of inheritance for color blindness in this family? autosomal recessive x-linked recessive autosomal dominant x-linked dominant y-linked
The answer is x-linked recessive. It is apparent that the color blindness affects the males hence it's caused by a sex-linked recessive gene. Males have XY homologous chromosomes. The X sister chromosome has more genes than the Y sister chromosome, hence most males are hemizygous for sex linked genes. This means that even recessive genes on the X chromosome are likely to be expressed in males.
