What does it mean for a gene to be sex-linked?

A gene is termed sex-linked when it is located on one of the sex chromosomes, which are the X and Y chromosomes in mammals. This designation signifies that the inheritance patterns of such genes differ from those of genes located on autosomes (non-sex chromosomes). For instance, because males typically have one X and one Y chromosome, they will express whatever allele is present on their single X chromosome, whether it is dominant or recessive. In contrast, females have two X chromosomes, allowing them to potentially inherit two different alleles for genes located on the X chromosome, influencing the expression of those traits.

Sex-linked traits can show unique inheritance patterns, such as hemophilia or color blindness, which predominantly affect males due to the presence of only one X chromosome. Therefore, identifying a gene as sex-linked highlights its location on the sex chromosomes and indicates how its inheritance may differ from genes found on autosomes. This specific association with sex chromosomes is critical in genetics and helps explain differences in trait expression between males and females.