Question

In humans, attached earlobes are a dominant feature over free earlobes while hypertrichosis of the ear is a holandric ($Y$-linked) feature. A man with attached earlobes and extensive hair on pinna married a woman having free earlobes. The couple had one son with attached earlobes and hairy pinna, another son with free earlobes and hairy pinna and two daughters with attached earlobes. One of the daughters married a man with free earlobes and sparse hair on pinna. They had two sons. What would be the characteristics of their pinnae ?

• A. Both will have attached earlobes and sparse hair on pinna
• B. There would be equal chances for both having free or attached earlobes and sparse hair on pinnae
• C. They would have hairy pinnae and there would be $1$ in $8$ chance that both will have attached earlobes
• D. Both will have free earlobes and extensive hair on pinnae

Answer 1

Answer: (B)

It is given that attached earlobes are a dominant feature hence, we can represent it as $LL$ or $LI$. Also, hypertrichosis of the ear is a $Y$-linked feature and thus we can represent is as $Y^h$. Now, according to the given information following crosses can be made :


Thus, there would be equal chances for both daughters and sons to have free earlobe (II) or attached $(LI)$ earlobe and sparse hair on pinna.