Question

Define sex linked inheritance. Explain it with haemophilia and colourblindness.

Hint:

In sex-linked inheritance, traits are passed through the X chromosome. Males are more often affected because they have only one X chromosome, while females have two, which can compensate for one defective X.

Answer 1

Sex-linked inheritance:
Sex-linked inheritance refers to the inheritance pattern of genes located on the sex chromosomes, typically the X chromosome. In humans, males have one X and one Y chromosome (XY), whereas females have two X chromosomes (XX). This difference results in different inheritance patterns for males and females. Males are more often affected by sex-linked disorders because they have only one X chromosome, while females have a second X chromosome to potentially compensate for the defective gene.
Haemophilia:
Haemophilia is a sex-linked recessive disorder. The gene responsible for haemophilia is located on the X chromosome. Males with the defective gene on their single X chromosome will express the disease because they have no second X chromosome to mask the defective gene. Females, on the other hand, would need to inherit the defective gene on both X chromosomes to exhibit the disease. If a female inherits the defective gene on only one X chromosome, she becomes a carrier and does not show symptoms of the disease.
Colourblindness:
Colourblindness is another example of a sex-linked recessive disorder. The gene for colour vision is located on the X chromosome. Like haemophilia, males with the defective gene on their single X chromosome will be colourblind. Females need to inherit two copies of the defective gene (one from each parent) to be colourblind. A female with only one defective copy will be a carrier but not affected by the condition.