Y-linked genes are transmitted from father to son to grandson.
Genes that are present in the unique region of the Y chromosome (the part that cannot cross over with the X) are known as Y-linked genes, of which there are not many. As well as the SRY male-determining gene, they include a number of genes in which mutations are associated with impaired fertility and low sperm count.
The pedigree characteristics of Y-linked inheritance are striking (Fig. 17.13):
- Only males are affected with the trait.
- Females never inherit or transmit the trait, regardless of how many affected male relatives they have.
- All sons of affected males are also affected.
FIG. 17.13 Inheritance of Y-linked traits. The pedigree pattern is that of father to son to grandson to great-grandson, and so forth.
Because the Y chromosome is always transmitted from father to son (and never transmitted to daughters), a trait determined by a Y-linked gene will occur in fathers, sons, grandsons, and so forth. Traits resulting from Y-linked genes cannot be present in females nor can they be transmitted by females. However, other than maleness itself and some types of impaired fertility, no physical traits are known that follow a strict Y-linked pattern of inheritance. This observation emphasizes the extremely low density of functional genes in the Y chromosome.