Human y chromosome


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Sex Chromosomes Evolution in Mammals

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Human y chromosome

  1. 1. Alireza zenhari
  2. 2.      58 million base pairs (the building blocks of DNA) 1% of the total DNA in a male cell contains 86 genes, which code for only 23 distinct proteins Acrocentric Smaller than X
  3. 3. Y  X  Y X Y Y   
  4. 4.   The human Y chromosome is unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions at the telomeres (which comprise about 5% of the chromosome's length). The bulk of the Y chromosome which does not recombine is called the "NRY" or nonrecombining region of the Y chromosome.
  5. 5. Sex chromosome aberrations 47 ,XXY Klin efelte r sy n dr ome m ale tall st atur e teste s do no t ma tu re ste ril e lowe red IQ is co mm on 1/700 m ale bir th s 45 ,X T u rn er S y nd rom e (X O) fem ale sho rt stature rud im e ntary ova ri es ste ril e IQ typ ica ll y nor m al 1/3000 fem ale b irth s 47 ,XYY Do ubl e-Y sy n dr om e m ale above ave rage he igh t, o the rw ise pheno typ ica ll y no rm al. A t one time , it wa s claim ed tha t X Y Y m ales are pron e to v io len t or an ti so c ial behav ior, ba sed on eleva ted inc idenc e o f 47 ,XYY a m ong inca rce rated m en. N ow though t to be du e to h igh e r inc idence of m ode rate m en tal re tarda ti on than for XY m ales . 47 ,XXX T riso m y -X syn d ro m e m any pheno typ ica ll y no rm al the frequency of lowe red IQ is h igher than am ong XX fe m al es .
  6. 6. ◦ These regions are called the pseudoautosomal regions., PAR1 and PAR2. ◦ a crossover in PAR1 is necessary in male meiosis to get proper segregation of the chromosomes.
  7. 7. AZF1 (azoospermia factor 1) BPY2 (basic protein on the Y chromosome) DAZ1 (deleted in azoospermia) DAZ2 PRKY (protein kinase, Y-linked) RBMY1A1 SRY (sex-determining region) TSPY (testis-specific protein) USP9Y UTY (ubiquitously transcribed TPR gene on Y chromosome) ◦ ZFY (zinc finger protein) ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦
  8. 8. Sex-determining Region on the Y SRY Y SRY DNA X SRY swyer  
  9. 9. SHOX   pseudoautosomal USP9Y AZFA    
  10. 10.      large submetacentric 1100 gene One of 2 X is inactive Most gene are unrelated to sex XIST (X Inactive Specific Transcripts)
  11. 11. Xq13 X X Inactive Specific Transcripts XIST X X Xq Xp
  12. 12. Barr X  Barr Body  X
  13. 13. X Mary Lyon  X X X X X X   
  14. 14. X SiRNA or Small interference RNA X RNA X SiRNA X X   H X  X X Anti Hemophilia Factor   
  15. 15. • Female mammals have an XX genotype. – Expression of sex-linked genes is similar to autosomal genes in females. – X chromosome inactivation randomly “turns off” one X chromosome – ensures that females, like males, have one functional copy of the X chromosome in each body cell X
  16. 16.      The Y chromosome was identified as a sexdetermining chromosome by Nettie Stevens at Bryn Mawr College in 1905 during a study of the mealworm Tenebrio molitor Hermann Henking the Y chromosome was the pair of the X chromosome . Stevens named the chromosome "Y" simply to follow on from Henking's "X" alphabetically That was depond on it shape
  17. 17. Y  X Y  X Y Y  Y X  X Y
  18. 18. Sex Chromosome Evolution: Y as Rotting X SRY A pair of autosomes X Y SRY X Y SRY X Y
  19. 19.    Most mammals have only one pair of sex chromosomes in each cell. Males have one Y chromosome and one X chromosome, while females have two X chromosomes. In mammals, the Y chromosome contains a gene, SRY, which triggers embryonic development as a male Exception of SRY mammals the platypus(similarity) with the avian Z chromosome
  20. 20.    The X and Y chromosomes are thought to have evolved from a pair of identical chromosomes termed autosomes Until recently, the X and Y chromosomes were thought to have diverged around 300 million years ago However, research published in 2010, and particularly research published in 2008 documenting the sequencing of the platypus genome,has suggested that the XY system would not have been present more than 166 million years ago
  21. 21.   Over time, the Y chromosome changed in such a way as to inhibit the areas around the sex determining genes(SRY) from recombining at all with the X chromosome. As a result of this process, 95% of the human Y chromosome is unable to recombine The tips of the Y chromosome that could recombine with the X chromosome are referred to as the pseudoautosomal region.
  22. 22.  By one estimate, the human Y chromosome has lost 1,393 of its1,438 original genes over the course of its existence, and linear extrapolation of this 1,393 gene loss over 300 million years gives a rate of genetic loss of 4.6 genes per million years. Continued loss of genes at the 4.6 genes per million year rate would result in a Y chromosome with no functional genes that is the Y chromosome would lose complete function within the next 10 million years. Comparative genomic analysis, however, reveals that many mammalian species
  23. 23.  The Y chromosome is passed exclusively through sperm, which undergo multiple cell divisions during gametogenesis. Each cellular division provides further opportunity to accumulate base pair mutations. Additionally, sperm are stored in the highly oxidative environment of the testis, which encourages further mutation. These two conditions combined put the Y chromosome at a greater risk of mutation than the rest of the genome
  24. 24.   Without the ability to recombine during meiosis, the Y chromosome is unable to expose individual alleles to natural selection. Deleterious alleles are allowed to "hitchhike" with beneficial neighbors, thus propagating maladapted alleles in to the next generation. Conversely, advantageous alleles may be selected against if they are surrounded by harmful alleles (background selection). Due to this inability to sort through its gene content, the Y chromosome is particularly prone to the accumulation of "junk" DNA. Massive accumulations of retrotransposable elements are scattered throughout the Y.[10] The random insertion of DNA segments often disrupts encoded gene sequences and renders them nonfunctional. However, the Y chromosome has no way of weeding out these "jumping genes". Without the ability to isolate alleles, selection cannot effectively act upon them. A clear, quantitative indication of this inefficiency is the entropy rate of the Y chromosome. Whereas all other chromosomes in the human genome have entropy rates of 1.5–1.9 bits per nucleotide (compared to the theoretical maximum of exactly 2 for no redundancy), the Y chromosome's entropy rate is only 0.84.[18] This means the Y chromosome has a much lower information content relative to its overall length; it is more redundant.
  25. 25.  Even if a well adapted Y chromosome manages to maintain genetic activity by avoiding mutation accumulation, there is no guarantee it will be passed down to the next generation. The population size of the Y chromosome is inherently limited to 1/4 that of autosomes: diploid organisms contain two copies of autosomal chromosomes while only half the population contains 1 Y chromosome. Thus, genetic drift is an exceptionally strong force acting upon the Y chromosome