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Chapter 14

BIOB11H3 Chapter Notes - Chapter 14: Metaphase, Robin Holliday, Genetic Recombination

Biological Sciences
Course Code
Dan Riggs

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Chapter 14 Cellular Reproduction
14.3 Mitosis
- Meiosis (Greek-reduction): Formation of production
of haploid phase in life cycle, fertilization ensures
diploid phase
- Diploid G2 cells contain pairs of homologous x-some, each
containing 2 x-tids
-During meiosis, 4 x-tids of a pair of replicated homologous
x-somes are distributed among 4 daughter nuclei
incorporates 2 division w/I intervening round of DNA
- In 1st meiotic division, each x-some/2 chromatids are
separated from homologue each daughter cell has 1
member of each pair of c-somes x-somes are paired
during prophase of I meiotic division (x-tids engage in
genetic recombination metaphase I)
- In 2nd meiotic division, 2 x-tids of each x-some are
separated from 1 another (anaphase II)
- Marked differences b/w stage w/I life cycle:
1. Gametic or terminal meiosis: Includes all
multicellular animals and many protists meiotic
division closely linked to formation of gametes (i.e.
male vertebrate meiosis occurs just prior to
differentiation of spermatozoa; vertebrate eggs are
fertilized at stage before completion of meiosis)
2. Zygotic or Initial Meiosis: Only protists and fungi:
Meiotic division occurs after fertilization to produce
haploid spores
3. Sporic or Intermediate Meiosis: Plants and some
algae meiotic division take place at stage unrelated
to gamete formation of fertilization
Sporophyte: Diploid zygote undergoes mitotis and
develops into this
Gametophyte: Sporophyte produces spores that
germinate to haploid gametophyte
Gametes are produced by mitosis
The Stages of Mitosis
- Prelude to meiosis DNA replication
- S phase: Several times longer than premitotic S phase
1. Prophases of 1st meiotic division lengthened in
extraordinary fashion
1st stage is leptotene, x-some visible in light
2nd stage is zygotene marked by visible association of
homologues w/ one another
Electron micrographs indicate x-some synapsis is
accompanied by formation of synaptonemal complex/SC:
structure w/
protein filaments
connectin 2
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