Sex chromosomes are not only relevant for sex determination. They carry genes that are associated with other traits. Thus, it is not uncommon to see certain traits manifesting as sex-linked. In humans and other animals, there are two types of sex-linked inheritance: (1) X-linked inheritance and (2) Y-linked inheritance.
Y-linked inheritance is a form of inheritance for the genes located on the Y chromosome. In human and other mammalian males, the sex chromosomes are the X and Y chromosome. Y chromosome is smaller than the X chromosome and thus, carries relatively fewer genes. Apart from the genes for sperm development, appropriate hormonal output, and other traits characterizing males, the Y chromosome also carries genes other than for sex determination.
Hypertrichosis of the ears, webbed toes, and porcupine man are examples of Y-linked inheritance in humans. Hypertrichosis of the ears (or hairy ears) is a condition wherein there is a conspicuous growth of hair on the outside rim of the ear. Webbed toes condition is characterized by having web-like connection between second and third toes. Porcupine man is a condition when the skin thickens and gradually becomes darker, scaly, rough, and with bristle-like outgrowths. Since Y-linked inheritance involves the Y chromosome, Y-linked inheritance is passed on from father to son.
- Holandric inheritance