Question

In the cells of all human females, one X chromosome is inactivated. The opsin1 gene is on the X chromosome and is expressed in the retinal cells of the eye. Mutations in this gene cause the recessive trait of colorblindness. Most women who have one mutant allele of the opsin1 gene and one normal allele of the opsin1 gene (they are heterozygous) can still see color. What is the most likely explanation for this finding? a. The X with the mutant allele of the opsin1 gene is more likely to be inactivated because of the opsin1 mutation. b. Any mutations in the opsin1 gene on the active X can be corrected through genetic exchange (recombination) with the inactive X. c. If the active X has the mutant allele of opsin1 gene, the inactive X with the normal allele will be reactivated. d. Some retinal cells will have an active X with the mutant allele of the opsin1 gene, and some will have an active X with the normal allele of the opsin1 gene.

Answer 1

d. Some retinal cells will have an active X with the mutant allele of the opsin1 gene, and some will have an active X with the normal allele of the opsin1 gene.

Step-by-step explanation:

X-inactivation (or silencing of X chromosome) is a process that occurs in females in order to prevent females from having twice as many X chromosome gene products as males. It occurs randomly during the embryonic development. Another important characteristic of X chromosome inacativation is that it occurs on a cellular level which leads to mosaic expression. This means that some cells will have an inactive maternal X-chromosome and some inactive paternal X-chromosome.