NATS 1675 Lecture Notes - Lecture 3: Spermatogenesis, Sister Chromatids, Mitochondrion

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6 Feb 2016
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NATS 1675
- MEIOSIS PHASES 2016-02-04 16:35
Phases of Meiosis:
(1) Prophase I:
Similar to mitosis with 2 major exceptions:
o 1. Synapsis
o 2. Crossover
Synapsis: The pairing or coming together of homologous
chromosomes to form a TETRAD (See image below)
Coming together of “like” chromosomes
Crossover: Homologous recombination is the process by which two
chromosomes, paired up during prophase 1 of meiosis, exchange
some distal portion of their DNA.
Can occur during synapsis
Equal portions of non-sister chromatids can be exchanged
Exchange of equal material
The purpose of crossover is to further increase genetic
variability in gametes
Crossing over can be replaced in the middle of the chromatids as
well and not only at the ends
Tetra
d'
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NATS 1675
- MEIOSIS PHASES 2016-02-04 16:35
In General: 23 2x2x2 = 8
For Humans: 223 = > 8 million
o Females: +/- 8 million eggs
o Males: +/- 8 million sperm
(2) Metaphase I:
Homologous pairs of chromosomes (those that have undergone
synapsis) line up on the equatorial plate
Chiasma'
Centromere''
Equatorial'Plate'
Centriole'
Spindle'Fibers'
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