Question

Color blindness is a recessive trait on the X chromosome. What are the genotype and phenotype ratios of a cross between a normal female who is not a carrier and a color-blind male?

Answer 1

In a cross between a normal female who is not a carrier and a color-blind male, all offspring will have normal color vision with a genotype ratio of 1:1 and a phenotype ratio of 100% normal color vision.

Step-by-step explanation:

Color blindness is a recessive trait located on the X chromosome. In a cross between a normal female who is not a carrier (XX) and a color-blind male (XcY), where Xc represents the allele for color blindness, we can predict the following outcomes:

• All daughters (XX or XcX) will have normal color vision because they inherit one normal allele from their mother and the only X chromosome from their father doesn't contain the normal color vision allele but does not express color blindness as the normal allele from the mother is dominant.
• All sons (XY) will have normal color vision because they inherit their X chromosome from their mother and the Y chromosome from their father.

The genotype ratio for this cross is 1:1 (XcX:XX for daughters and XY:XcY for sons). The phenotype ratio is 100% normal color vision for both daughters and sons.

Since the cross involves a non-carrier mother, none of the offspring will be color-blind, and the daughters are not carriers. Thus, there is no chance of color-blind offspring in this generation, reflecting the patterns of X-linked recessive inheritance.

Answer 2

if we cross XNXN(normal, non-carrier female) with XnY(color-blind male)

we get XNXn XNY XNXn and XNY

genotype ratio: XNXn:2 XNY:2

phenotype ratio:2 carrier females and 2 healthy males