Question

A woman is a carrier for red-green colour blindness. Her genotype is XcX where Xc indicates the chromosome with the allele conferring colour blindness and X indicates the chromosome with the normal colour vision allele. Very early in development, the Xc chromosome was inactivated in the first cell of her right eye. At the same time, the normal X chromosome was inactivated in the first cell of her left eye. Is she colour blind in her left eye, her right eye, both eyes, or neither eye?

Answer 1

As said in the problem the trait that causes blindness is located in one of the X chromosomes (Xc). If this chromosome is inactivated in one of the eyes, we can expect that the functions can be covered by the genes of the other chromosome X but also we can expect that there will be no blindness because the gene is not present. The same we can expect when the normal chromosome X is inactivated (there will be blindness because the gene is present and active). Therefore, she is color-blind only in her left eye