Which of the following most appropriately describes haemophilia ?
- X-linked recessive gene disorder
- Chromosomal disorder
- Dominant gene disorder
- Recessive gene disorder
The Correct Option is A
Solution and Explanation
Option 1: X-linked recessive gene disorder
Explanation:
Haemophilia is a genetic disorder that impairs the blood's ability to clot. This disorder is caused by a deficiency in one of the clotting factors, which is essential for proper blood coagulation.
- X-linked recessive gene disorder: Haemophilia is inherited through the X chromosome, and the gene responsible is recessive. This means that males (who have only one X chromosome) are more likely to express the disorder, while females (who have two X chromosomes) are more likely to be carriers unless both X chromosomes are affected.
- Chromosomal disorder: Haemophilia is not a chromosomal disorder as it is caused by mutations in a single gene, not an entire chromosome.
- Dominant gene disorder: Haemophilia is not a dominant disorder; it is recessive, meaning the affected individual needs to inherit two copies of the mutated gene (one from each parent) to express the condition (in females). In males, inheriting the mutated gene from just one parent is enough to express the disorder.
- Recessive gene disorder: While it is recessive, it is specifically **X-linked**, meaning it is carried on the X chromosome, which makes it more accurately described as an X-linked recessive gene disorder.
Thus, the correct answer is: X-linked recessive gene disorder.
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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.