This is the last type of genetics that will be shown because of how complex it is. Sex-linked genetics is referred to as a gene located in the sex chromosome. When a gene is found with an X chromosome and not a Y chromosome, it is sex-linked. This is because the gene controlling the trait is located on the sex chromosome, sex linkage is linked to gender. Therefore, females will have two copies of the sex-linked gene (XX) while males will only have one copy of this gene (XY). Sex-linked conditions are things that are passed on by sex chromosomes, such as : Red-green colorblindness, Male Pattern Baldness, Hemophilia, & Duchenne Muscular Dystrophy.
Before starting a sex-linked problem, you should know the following about humans :
Here is an example for X-linked:
In humans, hemophilia is a sex-linked condition and normal blood clotting (H) is dominant to the condition of hemophilia (h). A woman with hemophilia marries a normal man. What are the probabilities of them having children with hemophilia and their sexes?
According to this square, we know that there is a 50% chance of them having children with hemophilia, both male.