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Lecture 2

Biology 1201A Lecture Notes - Lecture 2: Aneuploidy, Chromatid, Sister Chromatids


Department
Biology
Course Code
BIOL 1201A
Professor
Jennifer Waugh
Lecture
2

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Origins of Variation Two
Meiosis – recombination, independent assortment at Me-I and Me-II
Errors – non-disjunction and misdivision, non-homologous and unequal
recombination
***Mitosis VS. Meiosis***
Dierences:
1. Genetic recombination only in
meiosis
2. Meiosis = 4 genetically unique daughter cells
3. Mitosis = 2 identical daughter cells
4. Prophase of
Meiosis
– pairing of homologous chromosomes
(tetrads)
5. Mitosis general occurs in somatic cells, Meiosis occurs in germ
(sex) cells
6. Meiosis – crossing over of chromosomes
7. Meiosis produces 4 haploid, Mitosis produces 2 diploid
8. Meiosis has 2 divisions, Mitosis has 1
9. Meiosis 1 separates homologous chromosomes, Mitosis
separates chromatids of chromosomes
Genetic Recombination
Physical exchange of sequences
between chromatids of homologous
chromosomes
Protein complex
(‘synaptonemal complex’)
forms between homologous
chromosomes
Segments of non-sister chromatids cross over, forming
“chiasmata” and are swapped
Results in new combinations of
alleles on chromosomes
Recombination Mechanism
One recombination event:
1. 4 DNA backbones are broken
2. Free ends are exchanged and
‘pasted’ together
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