What is sex linkage? Explain color blindness and haemophilia?

Sex linkage refers to the association of a trait with the sex of an individual because the gene controlling the trait is located on a sex chromosome. In humans, the X and Y chromosomes are the sex chromosomes.

Color blindness and haemophilia are examples of sex-linked traits because the genes responsible for these conditions are located on the X chromosome.

Color blindness is a condition where an individual has difficulty distinguishing between different colors, usually between greens and reds, and occasionally blues. This is due to a mutation in the genes that produce photopigments, the substances that detect color in our eyes. These genes are located on the X chromosome. Since males have only one X chromosome, if they inherit the X chromosome with the color blindness gene, they will be color blind. Females, on the other hand, have two X chromosomes, so even if they inherit one X chromosome with the color blindness gene, they can still have normal color vision if the other X chromosome has normal genes. This is why color blindness is more common in males than females.

Haemophilia is a disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding. This is due to mutations in the genes that produce clotting factors, proteins that are necessary for blood clotting. These genes are also located on the X chromosome. Similar to color blindness, if a male inherits the X chromosome with the haemophilia gene, he will have haemophilia. A female can only have haemophilia if she inherits two X chromosomes with the haemophilia gene, which is very rare. This is why haemophilia is more common in males than females.