Question

Some people have blue eyes, while others have brown. Two parents both having brown eyes have two children with blue eyes. Which of the following statements hold true regarding this?

• A. The allele for brown coloured eye is dominant.
• B. The probability of their next child having blue eyes is 50%.
• C. The probability of their next child having brown eyes is 75%.
• D. Both parents have one allele for blue eyes and one allele for brown eyes.

Answer 1

Answer: (A), (C), (D)

The correct options are
A The allele for brown coloured eye is dominant.
C The probability of their next child having brown eyes is 75%.
D Both parents have one allele for blue eyes and one allele for brown eyes.

$\bullet$ Since blue eyes were not expressed in either of the parents, it is a recessive trait. It shows that:

• Genotype of brown eyes: BB or Bb.
• Genotype of blue eyes: bb.

$\bullet$ In order to have a blue eyed offspring, brown eyed parents should have heterozygous condition (Bb) with one allele for brown eyes (B) and other for blue eyes (b).

$\bullet$ Out of 4 possible offsprings, the probability of having a child with brown-coloured eyes is 3/4 or 75% , while that of having blue-coloured eyes is 1/4 or 25%.