User:Dakotahodgson/sandbox

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

Current Article

 * 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

Y-linked Inheritance
The pattern of Y linked inheritance is due to a large lack of recombination between the X and Y chromosomes during meiosis. 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. 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. 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.

Testis-determining Factor
The sex determining region of the Y chromosome (SRY), found in the MSY, is commonly known as the testis-determining factor. SRY is known as such because its job is to induce the differentiation of bipotential gonads to produce testes. 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. 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. 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.

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

Azoospermia
Male infertility is often in the form of azoospermia, a condition in which there is no sperm in the ejaculate. 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).