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 ?

Updated On: Jul 6, 2022

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

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The Correct Option is B

Solution and Explanation

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.

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Notes on Principles of Inheritance and Variation

Concepts Used:

Principles of Inheritance and Variation - Mutation

A Mutation is a change in the sequence of our DNA base pairs caused by numerous environmental stimuli such as UV light or mistakes during DNA replication. Germline mutations take place in the eggs and sperm and can be passed onto offspring, whereas somatic mutations take place in body cells and are not passed on.

Types of Mutations

There are three types of mutations, which are as follows:

Silent mutation

It refers to any change in DNA sequence that has no effect on the amino acid sequence in a protein or the functions that a protein performs. There is no phenotypic indication that a mutation has occurred.

Nonsense mutation

When there is a change in the sequence of base pairs due to a point mutation, that results in a stop codon. This leads to a protein that is either shortened or non-functional.

Missense mutation

A missense mutation occurs when a point mutation causes a change in the codon, which then codes for another amino acid.

The mutation is caused by the following factors:

Internal Causes

When DNA copies incorrectly, the majority of mutations occur. Evolution occurs as a result of all of these mutations. DNA makes a copy of itself during cell division. When a copy of DNA isn't flawless, it's called a mutation since it differs somewhat from the original DNA.

External Causes

When certain chemicals or radiations are used to break down DNA, it causes the DNA to break down. The thymine dimers are broken by UV radiation, resulting in altered DNA.