Question

Joe is color blind. both his mother and his father have normal vision, but his mother's father (joe's maternal grandfather) is color 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

Answer 1

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.