The most typical kind of sex-linked inheritance occurs when a gene is found on the X chromosome. Due to the fact that females have two X chromosomes, they can inherit two copies of the gene from each parent and can either be homozygous (meaning both copies are the same) or heterozygous (meaning both copies are different) (both copies are different). Males, however, only inherit one copy of the gene because they have one X chromosome. Males are more susceptible to X-linked recessive illnesses as a result because they lack a second X chromosome to mitigate the impact of a bad mutation.

Hemophilia, colour blindness, and Duchenne muscular dystrophy are a few X-linked diseases. Only when the gene is found on the Y chromosome does Y-linked inheritance take place, which is much less common. Mother's genes have no impact on Y-linked features, which are only passed down from father to son. Hairy ears and one form of infertility are two examples of Y-linked characteristics.

Mutations in the genes that produce clotting factors, which are proteins that aid in blood clotting, result in hemophilia. Hemophilia is an X-linked recessive genetic condition, which means that the X chromosome contains the gene that causes the condition. Girls have two X chromosomes, therefore if they receive one copy of the faulty gene from a parent, they may be carriers of the illness. As males only have one X chromosome, they will acquire the disorder if they inherit a copy of the defective gene.

Another X-linked recessive genetic disease is colour blindness. The genes that produce the photopigments in the cone cells of the retina, which are the cells that detect colour, are mutated, leading to this condition. Depending on whether photopigment is harmed, there are many types of colour blindness.