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Size Doesn’t Matter

Size Doesn’t Matter. On T he Diminishing Y Chromosome By Michael Sistare. Some General Info. Genes determine physical characteristics Genes are contained in chromosomes You have 2 copies of 22 nonsex chromosomes 2 sex chromosomes – X+Y. The Sex Chromosomes. XX – female XY- male

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Size Doesn’t Matter

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  1. Size Doesn’t Matter On The Diminishing Y Chromosome By Michael Sistare

  2. Some General Info • Genes determine physical characteristics • Genes are contained in chromosomes • You have 2 copies of 22 nonsex chromosomes • 2 sex chromosomes – X+Y

  3. The Sex Chromosomes • XX – female • XY- male • Extent to which gender is expressed (more facial hair on a guy, e.g.) • Mom always donates an X • Dad either donates an X or a Y

  4. The Y Chromosome • Contains SRY gene (very important) • Presence of Y turns embryo male, lack of Y leaves embryo female • Contains other male-oriented genes • RBM1, DAZ and TSPY are genes on Y that code for spermatogenesis

  5. The Y Chromosome • Determines “maleness” – only main function • Evidence shows it used to be bigger • Could degenerate until it’s gone 

  6. The Y Chromosome Is Shrinking! • 300 million years ago, it was the same size as the X chromosome (1438 genes) • Has been shrinking at the rate of 4.6 genes per million years • Now has lost all but 45 remaining genes

  7. The Y Chromosome Is Shrinking!

  8. “The Degenerate Y Chromosome” • Paper published by Jennifer A. Marshall Graves • Research School of Biological Sciences, The Australian National University • Asserts that a new species of hominid could arise once it is gone!

  9. Reasons for Degeneration • Deletion (shrinkage) is possible in every generation! (telomeric region) • High rate of recurrent deletion – esp. in gene coding for spermatogenesis • 1% of men are infertile because of this deletion! – degeneration is affecting us now • The more deletions occur, the more unstable it is!

  10. What Will Happen If It Disappears? • Male gender will disappear • New species? • New means of reproduction? • Unisex bathrooms? • Genetic diversity – the purpose of procreation

  11. But Wait! There’s Hope! • NY Times Article - “Genetic Maker of Men Is Diminished but Holding Its Ground, Researchers Say” • http://www.nytimes.com/2012/02/23/science/y-chromosome-though-diminished-is-holding-its-ground.html?_r=1&ref=scienceandtechnology • Paper referenced a report in Nature entitled “Strict evolutionary conservation followed rapid gene loss on human and rhesus Y chromosomes”

  12. Nature Paper • Research suggests that the size of Y chromosome is stabilizing • It has only lost one gene in the last 25 million years • 25 million years ago – humans and Rhesus macaque monkey diverged from common ancestor

  13. Nature Paper • Hasn’t lost any genes in the past 6-7 million years! • Y genes don’t associate with other chromosomes • Y genes don’t get deleted • Genes on the Y chromosome are protected

  14. N(t)=(No-b)e-Kt+b • The Paper derived this equation to figure out how the Y chromosome would degenerate • Exponential decay plus a baseline! • Thanks to b, the mathematical model for the size of the Y will never drop below a certain number!

  15. The Y Chromosome Is Stabilizing! Hooray!

  16. Why Isn’t The Y Chromosome Shrinking Like We Thought? • Genes at the tips of chromosomes interact with other chromosomes through base-pairing (sequence-dependent) • This interaction can lead to detrimental effects (deletions, shortening)

  17. Why Isn’t The Y Chromosome Shrinking Like We Thought? • Y used to take part in this interaction with other chromosomes • Over time, Y’s genes were removed, then reintroduced into the chromosome upside-down • The new gene orientation disables proper base-pairing

  18. Why Isn’t The Y Chromosome Shrinking Like We Thought? • Since base-pairing can’t occur, the genes on Y are “protected” from detrimental interactions with other chromosomes • As a result, Y won’t continue shortening like it has been

  19. What Does This Mean For Us? • Y isn’t on a path to its own destruction • Puts to rest the notion of the disappearing Y chromosome (so fear not, dudes) • Even if Y loses more genes, the important genes are protected and probably won’t be lost

  20. So No Matter What They Tell You…Size Doesn’t Matter(Shape Does, Though )

  21. Citations • Wade, Nicholas. "Genetic Maker of Men Is Diminished but Holding Its Ground, Researchers Say." Nytimes.com. 22 Feb. 2012. Web. 25 Feb. 2012. <http://www.nytimes.com/2012/02/23/science/y-chromosome-though-diminished-is-holding-its-ground.html?_r=1&ref=scienceandtechnology>. • Marshall Graves, Jennifer A. "The Degenerate Y Chromosome – Can Conversion save It?" Reproduction, Fertility and Development 16.831 (2004): 527-34. CSIRO Publishing. Web. 25 Feb. 2012. <http://http://dx.doi.org/10.1071/RD03096>. • “Sex-chromosome picture” – karakalpak.com/genetics.html • Hughes, Jennifer F. "Strict Evolutionary Conservation Followed Rapid Gene Loss on Human and Rhesus Y Chromosomes." Nature (2012). Web. 28 Feb. 2012. <http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10843.html>.

  22. Citations • http://www.google.com/imgres?q=y+chromosome+sry&um=1&hl=en&client=firefox-a&sa=X&rls=org.mozilla:en-US:official&biw=1024&bih=470&tbm=isch&tbnid=ezUBb5mOmpx4SM:&imgrefurl=http://www.mun.ca/biology/desmid/brian/BIOL3530/DB_Ch12/DBNGerm.html&docid=CeKbo7fQiieutM&imgurl=http://www.mun.ca/biology/desmid/brian/BIOL3530/DB_Ch12/fig12_1.jpg&w=324&h=253&ei=lPNMT6_WD4yutwfg0fke&zoom=1&iact=hc&vpx=667&vpy=159&dur=1465&hovh=198&hovw=254&tx=141&ty=152&sig=109070860457074283393&page=1&tbnh=132&tbnw=169&start=0&ndsp=11&ved=1t:429,r:9,s:0

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