Unit 9: Meiosis

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25 Terms

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purpose of cell cycle

cell division: cells divide to:

reproduce (unicellular), grow (multicellular), repair/replace old/dead or damanged cells OR inc genetic diversity → product of meiosis is different from OG cell and eachother

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asexual vs sexual reproduction

Asexual reproduction: genetically identical offspring, single parent, no sperm or egg, only uses mitosis

Sexual: genetically unique offspring, two parents, fertilization of egg w/ sperm, uses meiosis

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binary fission

prokaryotic version of asexual reproduction by division in half (vs mitosis in plants also asexual)

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diploid cells

have 2 sets of chromosomes, 1 from each parent, and are body cells (2 versions of one gene/allele)

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haploid cells

have a single set of chromosomes, and are sperm and egg cells (1 versions of one gene/allele)

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sperm cells come from the

testies and have 23 chromosomes

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egg cells come from the

ovaries and have 23 chromosomes

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sperm and egg cells are called

gametes

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sperm + egg cells make

a zygote

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cell cycle for meiosis

cycle of growth (replication) + then division into 4 haploid cells

Interphase: 90%

  • G1 → growth

  • S → DNA synthesis (complete copy)

  • G2 → Growth & preparation for mitosis

Reduction Division of Cell

  • M I → MEIOSIS I (PMAT)

  • M II → MEIOSIS II (PMAT)

Division of Cytoplasm

  • C → continue cycle or Cytokinesis

<p>cycle of growth (replication) + then division into 4 haploid cells</p><p>Interphase: 90%</p><ul><li><p>G1 → growth</p></li><li><p>S → DNA synthesis (complete copy)</p></li><li><p>G2 → Growth &amp; preparation for mitosis</p></li></ul><p>Reduction Division of Cell</p><ul><li><p>M I → MEIOSIS I (PMAT)</p></li><li><p>M II → MEIOSIS II (PMAT)</p></li></ul><p>Division of Cytoplasm</p><ul><li><p>C → continue cycle or Cytokinesis</p></li></ul><p></p>
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Development of the chromosomes thru cell cycle

G1 (growth) → { } X X 46 chromosomes (homologous chromosome pair)

S (DNA synthesis) → X X X X “46” chromosomes (92 chromatids) (duplicated and linked as sister chromatids)

G2 (growth + prep) → review/ adjust chromosomes for errors

M (meiosis I & II) → division of chromosomes (anaphase) into 4 different haploid cells

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homologous chromosomes vs sister chromatids

G1 = homologous chromosome pairs from parents (not identical

S = sister chromatids are identical duplicated from 1 chromosome

<p>G1 = homologous chromosome pairs from parents (not identical</p><p>S = sister chromatids are identical duplicated from 1 chromosome</p>
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Meiosis

division of nuclear material to produce gametes

  • 5 major phases (PPMAT)

    • Prophase I & II

    • Prometaphase I & II

    • Metaphase I & II

    • Anaphase I & II

    • Telophase I & II

      • then cytokinesis (division of cytoplasm)

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Prophase I

1 - before

  • DNA begins to condense from chromatin → chromosomes/chromatid and line up with homologous pairs → each pair undergoes crossing (2 homologous chromosomes = tetrad (a group or set of four)

  • nuclear membrane + nucleolus dissolves

  • centrioles grow spindle fibers + push centrioles to poles

<p>1 - before</p><ul><li><p>DNA begins to condense from chromatin → chromosomes/chromatid and line up with homologous pairs → each pair undergoes crossing (2 homologous chromosomes = <strong>tetrad (</strong><span>a group or set of four)</span></p></li></ul><ul><li><p>nuclear membrane + nucleolus dissolves</p></li><li><p>centrioles grow spindle fibers + push centrioles to poles</p></li></ul><p></p>
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Crossing Over

part of Prophase

  • homologous chromosomes align in synapsis into tetrads (a group or set of four) (the pairing of homologous chromosomes)

  • chromosomes cross over

  • = recombinant chromatids

<p>part of Prophase</p><ul><li><p>homologous chromosomes align in synapsis into tetrads (<span>a group or set of four) </span>(the pairing of homologous chromosomes)</p></li><li><p>chromosomes cross over</p></li><li><p>= recombinant chromatids</p></li></ul><p></p>
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Prometaphase I

2

  • centriole spindles grow across cell connecting through centromere of each chromosome (forming kinetochore protein)

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Metaphase I

M - middle

  • chromosomes moved/align in middle IN PAIRS due to microtubules/spindle fibers

<p>M - middle</p><ul><li><p>chromosomes moved/align in middle IN PAIRS due to microtubules/spindle fibers</p></li></ul><p></p>
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Anaphase I

A - away

  • spindles shorten pulling apart HOMOLOGOUS CHROMOSOMES at centromere/kinetochore (but stay w/ sister chromatids) towards opposite poles

<p>A - away</p><ul><li><p>spindles shorten pulling apart HOMOLOGOUS CHROMOSOMES at centromere/kinetochore (but stay w/ sister chromatids) towards opposite poles</p></li></ul><p></p>
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Telophase I

5

  • once split chromosomes unravel to chromatin

  • spindles shorten into centrioles

  • nucleolus + nuclear envelope reforms

    • (cell wall pinches → cytokinesis)

<p>5</p><ul><li><p>once split chromosomes unravel to chromatin</p></li><li><p>spindles shorten into centrioles</p></li><li><p>nucleolus + nuclear envelope reforms</p><ul><li><p>(cell wall pinches → cytokinesis)</p></li></ul></li></ul><p></p>
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Interphase II

short resting phase for daughter cells

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Prophase II

1 - before the same except no crossing

  • DNA begins to condense from chromatin → chromosomes/chromatid and line up with homologous pairs → (no more crossing)

  • nuclear membrane + nucleolus dissolves

  • centrioles grow spindle fibers + push centrioles to poles

<p>1 - before the same except no crossing</p><ul><li><p>DNA begins to condense from chromatin → chromosomes/chromatid and line up with homologous pairs → (no more crossing)</p></li></ul><ul><li><p>nuclear membrane + nucleolus dissolves</p></li><li><p>centrioles grow spindle fibers + push centrioles to poles</p></li></ul><p></p>
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Prometaphase II

same except single file line

  • centriole spindles grow across cell connecting through centromere of each chromosome (forming kinetochore protein)

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Metaphase II

M - middle

  • chromosomes moved/align in middle SINGLE FILE due to microtubules/spindle fibers

<p>M - middle</p><ul><li><p>chromosomes moved/align in middle SINGLE FILE due to microtubules/spindle fibers</p></li></ul><p></p>
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Anaphase II

A - away

  • spindles shorten pulling apart SISTER CRHOMATIDS at centromere/kinetochore towards opposite poles

<p>A - away</p><ul><li><p>spindles shorten pulling apart SISTER CRHOMATIDS at centromere/kinetochore towards opposite poles</p></li></ul><p></p>
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Telophase II

  • once split chromosomes unravel to chromatin

  • spindles shorten into centrioles

  • nucleolus + nuclear envelope reforms

    • (cell wall pinches → cytokinesis)

<ul><li><p>once split chromosomes unravel to chromatin</p></li><li><p>spindles shorten into centrioles</p></li><li><p>nucleolus + nuclear envelope reforms</p><ul><li><p>(cell wall pinches → cytokinesis)</p></li></ul></li></ul><p></p>