Y-linkage, which can also be known as sex linkage, affects traits that are located on the Y chromosome.
For a trait to exhibit Y-linkage it must follow three requirements: the trait occurs in males only, it reoccurs in all sons of affected males, and that the daughters of affected men are not only phenotypically normal but also do not have affected offspring.
One trait that is known to be Y-linked occurs on spontaneously hypertensive rats. The trait is hypertension, which is composed of at least two loci in rats, one of which is autosomal while the other is Y-linked.
Y-linkage is very hard to determine and prove. The Y-chromosome is small and does not contain as many genes as autosomal genes or the X-chromosome. In the 1950s using human pedigrees, many genes were determined incorrectly to be Y-linked. Y-linkage has been disproved in many cases. Hairy ears were once thought to be Y-linked in humans; however, that hypothesis has been discredited.
Y-Chromosome deletions are a frequent genetic cause of male infertility.
Genes known to be contained on the Y chromosome
As of the year 2000, a number of genes were known to be Y-linked, including: