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Lecture 7

ANT203Y1 Lecture Notes - Lecture 7: Down Syndrome, Patau Syndrome, Allosome

Course Code
Julia Gamble

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Lecture 7: The Modern Study of Human Genetics
Sex chromosomes:
Trisomy 21: facial features that ar distinct for this syndrome
survival rate is high (age of mother imp)
Trisomy 13 and 18 are far more severe (dont survive as long)
XY can be either a female phenotype or an XX male phenotypes (some rare cases)
What leads to this pattern emerging? (happens during recombination: crossing over)
End up with some other chromosome material jumping off or on to the X chromosome (SRY
region on the Y chromosome codes for the production of sex characteristics: only a portion of Y
that is important to sex)
All continue to look female until SRY kicks in and stimulates testosterone (stimulates male
development in terms of sex)
cross over can make the SRY jump onto the X (now its on the X, not on the Y)
in XX males (X has a bit of the Y on it)
some parts of SRY code for sperm (if that part didn't jump onto the X, there will no
sperm production: there often not a gene linkage)
Potential causes for abnormal genotype/phenotype pairings:
XY female: either the SRY region is not acting up, its not on the Y anymore, could be due to
segregation during meiosis
Dont have determining factors to turn into male, even with the presence of Y chromosome
XXY: either the egg or the sperm had incomplete segregation, one of the gametes had two
chromosomes, may have had a sperm with xy or egg with xx
X: either egg or sperm didn't have a second chromosome
- We don't test for sex chromosomes unless there is a reason to, so understanding these diseases in
population is difficult (estimates are rough)
Can recognize foreign substances
Self antigens: markers on our own cells in red blood cells (blood types differ in the molecules
attached to their blood cells)
Blood group systems:
Eg. A negative : The A comes from the ABO system, while the negative comes from the Rh
ABO blood group:
A blood group produces antibodies for B (because B looks foreign to a)
AO (behave like an complete A)
AB: have both antigens A and B (neither looks foreign: can get A or B blood)
OO: group 0 – dont have a or b antigens (respond negatively to A and B)
universal donor is O (it doesnt have anything that A or B would react to)
but O would have neg reaction to A, B and AB
O does have an antigen: its H
AB are universal recipients
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