Question

In humans, blue eyes are inherited as a recessive autosomal trait and color blindness is an X-linked recessive trait. A woman with blue eyes and normal color vision whose father was color-blind marries a man who also has normal color vision. He has brown eyes but his mother had blue eyes. Which of the following would you expect to be TRUE for their daughters?A) One-half of their daughters will have normal color vision and brown eyes; 1/2 of their daughters will have normal color vision and blue eyes.
B) Their daughters will all have normal color vision and have blue eyes.
C)Their daughters will all have normal color vision and brown eyes.
D) One-fourth of their daughters will be color blind and have blue eyes, 1/4 of their daughters will be Color blind and have brown eyes, 1/4 of their daughters will have normal color vision and blue eyes, 1/4 of their daughters will have normal color vision and brown eyes.
E) One-half of their daughters will be color blind and have blue eyes; 1/2 their daughters will be color blind and have brown eyes.

Answer 1

Answer:

A) One-half of their daughters will have normal color vision and brown eyes; 1/2 of their daughters will have normal color vision and blue eyes.

Explanation:

The genotypes and phenotypes are:

• BB or Bb= brown eyes
• bb= blue eyes
• XᴰXᴰ, XᴰXᵈ (women) or XᴰY (men)= normal vision
• XᵈXᵈ (women) or XᵈY (men) = color blind

A woman has blue eyes (bb) and normal color vision (she has an Xᴰ chromosome) but her father was color-blind, so the other X chromosome she has carries the recessive d allele. She has the genotype bb XᴰXᵈ.

The man has normal color vision (he is XᴰY) and has brown eyes, but his mother had blue eyes so he must have inherited a b allele from her and is therefore heterozygous Bb. His genotype is BbXᴰY.

The blue/brown eyes gene is autosomal and independent from the sex-linked color blindness gene.

The woman can produce the gametes b Xᴰ and b Xᵈ.

The man can produce the gametes B Xᴰ, b Xᴰ, B Y and bY.

The female daughters can have the following genotypes and phenotypes:

• Bb XᴰXᴰ brown eyes, normal color vision
• Bb XᴰXᵈ brown eyes, normal color vision
• bb Xᴰ Xᴰ blue eyes, normal color vision
• bb Xᴰ Xᵈ blue eyes, normal color vision