Size Doesn*t Matter

Report
Size Doesn’t Matter
On The 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
• 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
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
The Y Chromosome
• Determines
“maleness” –
only main
function
• Evidence shows
it used to be
bigger
• Could
degenerate until
it’s gone 
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
The Y Chromosome Is
Shrinking!
1600
1400
1200
1000
800
Size of Y Chromosome
(Genes)
600
400
200
0
300
Million
years
ago
150
m.y.a
75
m.y.a
38
m.y.a
Now
“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!
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!
What Will Happen If It
Disappears?
• Male gender will
disappear
• New species?
• New means of
reproduction?
• Unisex bathrooms?
• Genetic diversity –
the purpose of
procreation
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/sc
ience/y-chromosome-though-diminishedis-holding-itsground.html?_r=1&ref=scienceandtechno
logy
• Paper referenced a report in Nature entitled
“Strict evolutionary conservation followed
rapid gene loss on human and rhesus Y
chromosomes”
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
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
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!
The Y Chromosome Is
Stabilizing! Hooray!
1600
1400
1200
1000
800
600
Size of Y Chromosome
(Genes)
400
200
0
300
150
75
38
25
Now
Million m.y.a m.y.a m.y.a m.y.a
years
ago
Why Isn’t The Y Chromosome
Shrinking Like We Thought?
• Genes at the tips of chromosomes
interact with other chromosomes
through base-pairing (sequencedependent)
• This interaction can lead to
detrimental effects (deletions,
shortening)
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
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
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
So No Matter What
They Tell You…
Size Doesn’t Matter
(Shape Does, Though )
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/ychromosome-though-diminished-is-holding-itsground.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/nat
ure10843.html>.
Citations
• http://www.google.com/imgres?q=y+chromosome+
sry&um=1&hl=en&client=firefoxa&sa=X&rls=org.mozilla:enUS:official&biw=1024&bih=470&tbm=isch&tbnid=ez
UBb5mOmpx4SM:&imgrefurl=http://www.mun.ca/
biology/desmid/brian/BIOL3530/DB_Ch12/DBNGe
rm.html&docid=CeKbo7fQiieutM&imgurl=http://w
ww.mun.ca/biology/desmid/brian/BIOL3530/DB_C
h12/fig12_1.jpg&w=324&h=253&ei=lPNMT6_WD4yu
twfg0fke&zoom=1&iact=hc&vpx=667&vpy=159&dur
=1465&hovh=198&hovw=254&tx=141&ty=152&sig=1
09070860457074283393&page=1&tbnh=132&tbnw=169
&start=0&ndsp=11&ved=1t:429,r:9,s:0

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