Question

Colorblindness is inherited with an X-linked recessive allele. Which term describes the genotype for a colorblind male?

1) XX
2) XY
3) XcXc
4) XcY

Answer 1

The genotype for a colorblind male is XcY. This is because colorblindness is an X-linked recessive trait and males express it if their single X chromosome carries the recessive allele. This condition is more common in males due to their XY chromosome composition.

Step-by-step explanation:

The genotype for a colorblind male is XcY.

Colorblindness is an X-linked recessive trait meaning it is carried on the X chromosome and requires a recessive allele to be expressed. Males have only one X chromosome and one Y chromosome, denoted as XY. If the X chromosome carries the recessive allele for colorblindness, denoted as Xc, the male will express the trait because there is no corresponding allele on the Y chromosome that can mask the recessive gene. Therefore, a colorblind male's genotype is represented by XcY.

Since females have two X chromosomes (XX), they must inherit recessive alleles on both X chromosomes to express the trait, which is relatively rare. That would result in a genotype of XcXc for a colorblind female. In contrast, females who carry one colorblindness allele and one normal allele, represented as XcX, do not express the trait but can pass on the recessive allele to offspring. This difference in genetic makeup explains why colorblindness is more prevalent in males than in females, as it affects about 1 in 20 males but only about 1 in 400 females.