10.5 Y-Linked Genes

In humans, the Y chromosome has been studied and is known to contain approximately 200 genes which provide instructions for making proteins. Because only males have the Y chromosome, the genes on this chromosome tend to be involved in male sex determination and development. Sex is determined by the SRY gene, which is the sex-determining region of the Y-chromosome.

Other genes on the Y chromosome are important for enabling men to father biological children (male fertility). Many genes are unique to the Y chromosome, but genes in areas known as pseudoautosomal regions are present on both sex chromosomes. As a result, men and women each have two functional copies of these genes. Many genes in the pseudoautosomal regions are essential for normal development.  Although the Y-chromosome is sex-determining in humans and some other species, not all genes that play a role in sex determination are Y-linked.

Y-linked traits, while few in number, do exist. For instance, the Y-linked trait of “webbed toes” causes a web-like connection between second and third toes, and “porcupine man” occurs 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. Of course, Y-linked traits never occur in females, and occur in all male descendants of an affected male. The concepts of dominant and recessive do not apply to Y-linked traits, as only one allele (on the Y) is ever present in any one (male) individual (this, is of course, ignoring XYY syndrome, which is a rare chromosomal disorder that affects males. It is caused by the presence of an extra Y chromosome. Males normally have one X and one Y chromosome. However, individuals with this syndrome have one X and two Y chromosomes).

Take a look at the video, Sex determination by the Y chromosome, by Genetics/ UC Davis (2017) on YouTube, which looks at sex determination by the Y-chromosome.

Media Attribution

• Figure 10.5.1 Y Chromosome by Christinelmiller, CC BY-SA 4.0, via Wikimedia Commons

Reference

Genetics/ UC Davis (2017, December 31). Sex determination by the Y chromosome (video file). YouTube. https://www.youtube.com/watch?v=Fd31_gaRyME

Long Description

• Figure 10.5.1 The structure of the Y-chromosome in humans shows pseudoautosomal regions at the ends, the position of the centromere, the short arm, which contains the loci for the SRY gene – the sex-determining region of the Y-chromosome, and the long arm. The Y chromosome contains approximately 59 million base pairs, and carries approximately 150 genes, and was identified as a sex chromosome in 1905. [Back to Figure 10.5.1]