Question:

If father shows normal genotype and mother shows a carrier trait for haemophilia:

Updated On: May 30, 2022
  • All the female offspring will be normal.
  • All the female offspring will be carriers.
  • A male offspring has 50% chances of active disease.
  • Female offspring has probability of 50% to have active disease.
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The Correct Option is C

Solution and Explanation

Haemophilia is a sex-linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progenies, hence shows criss - cross inheritance pattern. It is genetically due to recessive sex - linked gene h carried by X chromosome. A female becomes haemophiliac only when both its X chromosomes carry the gene$ (X^h X^h)$ whereas in case of males, a single gene for the defect is able to express itself $(X^h Y)$. If father is normal (X Y) and mother is carrier $(X^h X)$ then the probabilities for active disease in offsprings are illustrated in the cross given below:
Hence, a male offspring has 50% chance of active disease,
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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.