Question

Red-green color blindness is an X-linked recessive trait in humans. The dominant Xcn allele produces normal color vision, while the recessive Xcb allele produces color blindness. If a color-blind woman mates with a man who has normal color vision (P generation), what proportions of genotypes/phenotypes do you expect to see in their children (F1 generation)?

Answer 1

One half of their offspring will be girls with normal vision, and one half of their offspring will be color blind boys.

Step-by-step explanation:

Red-green color blindness is an X-linked recessive trait. The dominant Xcn allele produces normal color vision, while the recessive Xcb allele produces color blindness. Women have two X chromosomes, men have one X and one Y chromosomes.

The possible genotypes and phenotyes for this trait are:

• XcnXcn: normal woman
• XcnXcb: normal woman
• XcbXcb: color blind woman
• XcnY: normal man
• XcbY: color blind man.

A color-blind woman (XcbXcb) mates with a man with normal color vision (XcnY).

The woman only produces Xcb gametes, while the man produces two types of gametes: Xcn and Y.

The possible genotypes and phenotypes of their children resulting from the combination of those gametes are:

• 1/2 XcbXcn: normal vision daughters

• 1/2 XcbY: color blind sons

One half of their offspring will be girls with normal vision, and one half of their offspring will be color blind boys.