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Y linkage Wikipedia Article

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

Current Article

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  • 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

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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.[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]

Testis-determining Factor

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The Y chromosome, showing the location of the SRY gene

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]

Y-linked Male Infertility

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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]

Azoospermia

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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]

References

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  1. ^ a b c d Lahn, B (2001). "the human Y chromosome, in the light of evolution". Nature Reviews. 2.
  2. ^ a b Jangravi, Z (2013). "A fresh look at the male-specific region of the human Y chromosome". Journal of proteome research. 12.
  3. ^ a b c d Heard, E; Turner, J (2011). "Function of the sex chromosomes in mammalian fertility". Cold Spring Harbor Perspectives in Biology. 3.
  4. ^ Barrionuevo, F (2012). "Genes promoting and disturbing testis development". Histology and Histopathology. 27.
  5. ^ Quinn, A (2012). "The molecular genetics of sex determination and sex reversal in mammals". Seminars in Reproductive Medicine. 30.
  6. ^ Ferlin, A (2006). "Genetic causes of male infertility". Reproduction Toxicology. 22.
  7. ^ Ali, S; Hasnain, S (2003). "Genomics of the human Y-chromosome 1. Association with male infertility". Gene. 321.