Question

Red-green color blindness is due to a mutant gene in the X chromosome. An XX female with normal color vision and an XY male with normal color vision have a child with karyotype XXY who is color blind. The likely explanation is that the:_--------.

Answer 1

Red-green color blindness is due to a mutant gene in the X chromosome. An XX female with normal color vision and an XY male with normal color vision have a child with karyotype XXY who is color blind. The likely explanation is that the:_--------.

father was heterozygous for the color-blindness mutation.

mother was heterozygous for the color-blind mutation.

father had CNV of the color-blind mutation.

mother had CNV of the color-blind mutation.

None of the other answer options is correct.

Answer:

mother was heterozygous for the color-blind mutation.

Explanation:

Colorblindness is a recessive disorder. This means that it is expressed only in homozygous genotypes. The responsible gene is present on the X chromosomes. A colorblind female would have the genotype X^cX^c where c is the recessive allele of the gene present on the X chromosome responsible for color blindness. A female with genotype X^cX would have normal visible but would serve as a carrier.

Both the female and the male have normal genotype. Since they had a colorblind child, it means that the female was a heterozygous carrier for the trait and imparted the responsible allele to the child. The male can not serve as a carrier for X linked recessive disorder since they have only one copy of the X chromosome. Therefore, the female was a heterozygous carrier.