Explain sex-linked inheritance with examples.

Sex-linked inheritance refers to the transmission of traits that are controlled by genes located on sex chromosomes, most commonly the X chromosome. Since males (XY) have only one X chromosome, while females (XX) have two, the pattern of inheritance differs between them.

In X-linked recessive inheritance, a single recessive allele on the X chromosome is sufficient to express the trait in males because they lack a second X chromosome to mask it. Females, however, must inherit two copies of the recessive allele (one from each parent) to express the trait.

Common examples include:

• Hemophilia: a disorder affecting blood clotting

• Color blindness: inability to distinguish certain colors

For instance, if a mother is a carrier (one normal allele and one affected allele) and the father is normal, there is a 50% chance that sons will express the disorder and a 50% chance that daughters will become carriers.

In X-linked dominant inheritance, a single dominant allele on the X chromosome can cause the trait in both males and females, though females may show less severe symptoms.

Overall, sex-linked inheritance explains why certain genetic disorders are more common in males and follows patterns different from autosomal inheritance.