Important Genes Found Only on the X Chromosome and Their Functions

Important Genes Found Only on the X Chromosome and Their Functions

The X chromosome is larger than the Y chromosome and contains more than 1,000 genes.
Many of these genes are not found on the Y chromosome at all, and they are known as X-linked genes.
These genes play important roles in vision, blood clotting, muscle strength, brain development, and immunity.
Below are some well-known X-linked genes and the functions they perform:

1. OPN1LW and OPN1MW Genes

These genes are responsible for red and green colour vision.
When these genes are faulty or missing, the person may suffer from red-green colour blindness.
This condition is more common in males because they have only one X chromosome.

2. DMD Gene (Dystrophin Gene)

This gene helps in the production of dystrophin, a protein that protects muscle cells.
Mutation in this gene causes Duchenne muscular dystrophy, a severe muscle-wasting disease.
It affects boys mainly and leads to muscle weakness and difficulty in walking.

3. F8 Gene (Factor VIII Gene)

This gene is involved in the production of clotting factor VIII, which is essential for blood clotting.
When this gene is defective, it causes Haemophilia A, a disorder where blood does not clot properly.
Even a small injury can lead to excessive bleeding in affected individuals.

4. F9 Gene (Factor IX Gene)

This gene helps in making clotting factor IX, another important protein for blood clotting.
Its mutation leads to Haemophilia B, another type of bleeding disorder.
It also mainly affects males.

5. MECP2 Gene

This gene is crucial for brain development and helps control the activity of other genes in the brain.
Defects in this gene cause Rett syndrome, a serious neurological disorder that affects girls.
It leads to loss of movement, speech, and hand function after early childhood.

6. IDS Gene (Iduronate 2-sulfatase Gene)

This gene is needed to break down certain complex sugars in the body.
Mutation in this gene causes Hunter syndrome, which can lead to organ damage, mental retardation, and joint stiffness.
It is a rare and serious genetic disorder mostly affecting boys.

7. BTK Gene (Bruton's Tyrosine Kinase Gene)

This gene plays a key role in the immune system, especially in the production of B-cells (a type of white blood cell).
Mutations cause X-linked agammaglobulinemia (XLA), a condition where the body cannot make enough antibodies.
Affected boys suffer from frequent infections.

8. ABCD1 Gene

This gene helps in the transport and breakdown of very long chain fatty acids in the body.
Mutations lead to Adrenoleukodystrophy (ALD), a condition that affects the brain and spinal cord.
It causes symptoms like weakness, vision loss, and poor coordination.

9. AR Gene (Androgen Receptor Gene)

This gene helps the body respond to male sex hormones (androgens).
Defects in this gene cause Androgen Insensitivity Syndrome (AIS).
In this condition, a person is genetically male (XY) but their body cannot respond to male hormones, leading to female-like physical traits.

10. G6PD Gene (Glucose-6-phosphate dehydrogenase Gene)

This gene protects red blood cells from damage.
Mutation leads to G6PD deficiency, which causes sudden breakdown of red blood cells (called hemolysis), especially after certain infections or medicines.
It can result in anaemia and jaundice.

Summary

These X-linked genes are not present on the Y chromosome, so males have only one copy of each.
If that single gene is defective, males cannot rely on a backup copy, making them more likely to show the disorder.
Females have two X chromosomes, so if one gene is faulty, the other one can often make up for it.

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