Every human being has 46 chromosomes, including two chromosomes (X ,Y) that determine gender. The Y chromosome is unique to males. Inheriting an X chromosome from the mother and a Y chromosome from the father makes the child male. Because the Y chromosome is absolutely tied to maleness, defects in genes on this chromosome are mostly associated with Y chromosome infertility and defects in development of the male reproductive organs. Some forms of the disease retinitis pigmentosa have also been linked to Y chromosome inheritance.
Y chromosome infertility
Y chromosome infertility is a defect on the Y chromosome that results in a complete failure to produce sperm (azoospermia) or a partial defect in sperm production resulting in the production of much lower sperm numbers (oligospermia). If sperm are produced, they are often abnormally shaped and have no or poor swimming ability. Depending on the severity of Y chromosome infertility, men may be totally infertile or may require assisted reproductive technology procedures like sperm injection to father a child. Y chromosome infertility occurs in approximately 1 in 2,000 men. In men who are unable to produce sperm, 5 to 10 percent have Y chromosome infertility. There are several genes which have been linked to Y chromosome infertility, including CDY1, DAZ1, DAZ2, DDX3Y, HSFY1 and RBMY1A1.
Azoospermia or the complete inability to produce sperm can be caused by a deletion of the azoospermia factor (AZF) region. If the AZF region has deleted genes, the sperm production proteins can not be produced and sperm are not made. Within the AZF region is a specific gene called USP9Y, which if deleted, produces stunted non-functional versions of the sperm-making proteins, resulting in azoospermia.
Abnormal or Absent Testicular Development
The sex determining region Y (SRY) of the Y chromosome is specifically responsible for normal development of the male gonads (testicles). If this region is deleted, an XY individual will have a range of defects in testicular development (gonadal dysgenesis) often resulting in ambiguous genitalia or formation of female gonads. In some cases, true hermaphroditism (the presence of both a male and female reproductive tract organs) can result. Men with this deletion are usually infertile with little or no sperm production.
Retinitis pigmentosa is a genetically inherited disease of the eye in which the cells of the retina produce defective proteins. Symptoms include a progressive loss of sight starting with decreased night vision, followed by loss of peripheral or side vision and finally blindness. There is no treatment or cure. This disease is caused by mutations in the RPY (retinitis pigmentosa, Y-linked) gene, which cause it to make faulty versions of proteins needed for normal vision.