Question

Given above is a pedigree chart of a family with five children, It shows the inheritance of attached ear-lobes as opposed to the free ones. The squares represent the male and circles the female individuals. Which one of the following conclusions drawn is correct?

• A. Parents are homozygous dominant.
• B. Parents are heterozygous.
• C. Parents are homozygous recessive.
• D. Trait is Y-linked.

Answer 1

Answer: (B)

Parents are heterozygous.

As is visible trait skips generations; the unaffected parents have diseased progeny which means that the trait is present in recessive condition in parents. Thus, parents are heterozygous for the recessive trait and serve as carrier for it; option B is correct. If it was a dominant trait; the parents would have expressed it. If parents were homozygous dominant, the trait would express in parents also; but parents are not showing the trait which makes option A incorrect. If the parents were homozygous recessive; the trait would express due to absence of dominant gene, option C incorrect. An almost equal number of affected males and females occur which means that trait is not dependent of sex of individual; it is an autosomal trait which makes option D wrong. Correct answer is B.