BIOL 112 Lecture Notes - Lecture 6: Chromosome, Aneuploidy, Stochastic Process

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21 Jul 2016
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o!However, problems with this: Down's syndrome, happens more often with
older owmen
!!A problem with meiosis I; two homologues in one cell, so daughter
cells (from meiosis II) still have 2 of each chromosome (21 in this
case)
!!The older the mother, the longer the egg has been "sitting around", in
an arrested stage
!!And the longer the egg has been sitting around the greater the
chance of imperfect duplication
2.3Ploidy
!We're diplontic life organisms - mostly diploid, small haploid portion (fertilisation
etc)
!But there are also haplontic organisms, e.g. algae - almost completely haploid,
gametes fuse, undergo meiosis immediately (so briefly diploid I guess)
!It's not the absolute number of chromosomes that's important, but rather the ratio
that matters
!As long as the ratio is constant (e.g. 3 chromosome 1s, 3 chromosomes 3)
!However, odd ploidys tend to be sterile (one daughter cell will have more
chromosomes than the other etc)
!Trisomy: genetic anomaly, three copies (instead of two) of a particular chromosome
(type of aneuploidy)
!You can also have triploids (sterile though) and tetraploids or even more
o!For example, store-bought strawberries ... can be octoploids (makes them
bigger, still viable and fertile)
o!Another example: frog in South Africa, at one point, evolved to be tetraploid
rather than diploid (whole new species); similar but larger than original
3Genetics: Mendel
!Gregor Mendel: Austrian(/Australian) monk, really cool guy and doesn't afraid of
anything
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