BIOL1006 Lecture Notes - Lecture 5: Synaptonemal Complex, Fertilisation, Synapsis

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25 Jun 2016
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Lecture 4
fertilization - aka syngamy; fuses gametes to form a new cell
gametes - eggs, sperm
somatic cells - nonreproductive cells
has twice as many chromosomes as gametes
never form gametes
zygote - formed by 2 gametes fusing together
meiosis produces cells w/ 1/2 the normal number of chromosomes
sexual reproduction - uses meiosis/fertilization to give chromosomes
from 2 parents to offspring
23 maternal homologues from mother, 23 paternal homologues from
father in humans
life cycles of organisms w/ sexual reproduction alternate between
diploid/haploid periods
germ-line cells - will eventually produce gametes
undergoes meiosis, not mitosis
synapsis - close association of chromosomes during prophase I of
meiosis
synaptonemal complex - homologues paired closely along a protein
lattice between them
pairs of homologues come together during metaphase I
homologues, not sister chromatids, go towards opposite poles during
anaphase I
meiosis I - aka “reduction division”
crossing over - genetic recombination
homologues can exchange chromosomal information
chiasmata - sites of crossing over, maintained until anaphase I
continued association of chromosome pairs until anaphase is needed to
ensure accurate separation
2 divisions - genetic material only replicated once
produces cells w/ 1/2 the number of chromosomes
meiosis II - like mitosis, but without chromosome duplication
prophase I - DNA coils and becomes visible under light microscopes
sister chromatid cohesion - pairing of homologous pairs side by side
guided by heterochromatin sequences
homologues attach to nuclear envelope at specific sites
recombination nodules - has enzymes for breaking/joining
homologous chromatids
crossing over between sister chromatids is suppressed
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