User:Dakotahodgson/sandbox

This is a user sandbox of Dakotahodgson. A user sandbox is a subpage of the user's user page. It serves as a testing spot and page development space for the user and is not an encyclopedia article.

I am planning to edit the y linkage stub article as part of my course in advanced genetics here at UWO.

• basic definition of y linkage
• brief overview of inheritance of y linked genes
• small reference to infertility in males because of y chromosome deletions
• notes that the y chromosome is small and contains very few genes

The pattern of Y linked inheritance is due to a large lack of recombination between the X and Y chromosomes during meiosis.^[1] On the Y chromosome there are two pseudoautosomal regions (regions that have sequences homologous with the X chromosome, where recombination between X and Y can occur) on the ends of both the short p and long q arms^[1]. These regions can line up and recombine with homologous sequences on the X chromosome during meiosis, whereas the rest of the Y chromosome, approximately 95% known as the male specific region MSY, will not participate in recombination. ^[2] A gene is Y-linked when it lies within the MSY, and because of the complete lack of recombination in this region, Y linked genes, traits and disorders can only be passed from father to son. Protein coding genes in the MSY have a wide variety of biological functions, and although a great deal of them are male development and reproduction specific, many have roles in a multitude of other systems. ^[3]

The sex determining region of the Y chromosome (SRY), found in the MSY, is commonly known as the testis-determining factor. ^[1] SRY is known as such because its job is to induce the differentiation of bipotential gonads to produce testes.^[4] It is important to note that the SRY genes do have homologous sequences on the X chromosome. In males, the X homologs are active, whereas in females, the homologous sequences are inactivated on both X chromosomes.^[1] The active presence of testis-determining factor genes in an individual will induce male development. In the absence of testis-determining factor genes, female development will occur by default. ^[5] In rare cases, XY individuals can be female. This can be because an individual has a loss of function mutation in a SRY gene; even though they have a Y chromosome, without the testis determining factor, development will default to female.^[2]

Genetic abnormalities account for 15% of the cases of infertility in human males.^[6] These abnormalities have been attributed to aneuploidies or mutations of mainly the sex chromosomes, but also the autosomes.^[7] The Y chromosome has a significant role in male reproduction and development, and any alterations can be detrimental to these systems.^[3]

Male infertility is often in the form of azoospermia, a condition in which there is no sperm in the ejaculate.^[3] Azoospermia can be caused genetically by either sex chromosome abnormalities in the form of Turner Syndrome (where individuals have only one X chromosome), Klinefelter Syndrome (individuals with two X and one Y chromosomes) or Double Y Syndrome (individuals with one X and two Y chromosomes), or small Y chromosome deletions, known as microdeletions. The Y chromosome deletions that have been linked to infertility tend to occur in the azoospermia factor regions (AZF) of the Y chromosome classified into AZFa, b and c. Because the Y chromosome does not have a homologous chromosome to recombine with, these deletions often cannot be repaired. Deletions within any of these regions can result in a complete absence of sperm cells (AZFa), a block during meiosis (AZFb) or an arrest during spermatogenesis that produces a small number of incorrectly shaped sperm (AZFc – the most common). ^[3]