Meiosis Flashcards

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1
Q

Define meiosis

A
  • results in production of 4 daughter nuclei
  • all haploid, half number of chromosomes as parent cells
  • e.g. gametes
  • undergoes 2 nuclear divisions
  • aka reduction division
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2
Q

Why are gametes produced?

A
  • nucleus of male gamete and female gamete fuses during fertilisation (each is haploid)
  • form diploid number of chromosomes, maintained in zygote
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3
Q

Interphase

A
  • chromatin threads replicate to produce 2 identical sis chromatids
  • centrioles replicate
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4
Q

Prophase I

A
  • chromatin threads condense, coil and shorten into visible chromosomes
  • homologous chromosomes pair up (synapsis) , each pair is a bivalent
  • crossing over btw sis chromatids of homologous chromosomes may occur (exchange DNA)
  • point of cross over = chiasma
  • results in new combi of alleles along chromosomes
  • centrioles move to opp ends, nuclear envelope disintegrates, spindle fibres form
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5
Q

Metaphase I

A
  • homologous chromosomes arrange themselves along equator (orientation can vary)
  • one of each pair faces opp poles
  • each chromosome attached to spindle fibre
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6
Q

Anaphase I

A
  • homologous chromosomes separate

- one of each pair pulled to opp pole of cell

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7
Q

Telophase I

A
  • spindle fibres disintegrates
  • nuclear envelope reforms in animal cell only
  • most plant cells dont undergo telophase I, move straight to metaphase II)
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8
Q

Cytokinesis I

A
  • centrioles replicate (4)

- cytoplasm cleaves/splits to form 2 daughter cells (haploid)

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9
Q

Prophase II

A
  • centrioles move to opp poles of cell
  • nuclear envelope disintegrates
  • spindle fibres appear
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10
Q

Metaphase II

A
  • chromosomes line singly along equator

- homologous chromosomes lie next to each other (unlike metaphase I)

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11
Q

Anaphase II

A
  • centromeres divide, sis chromatids separated to becomes daughter chromosomes
  • daughter chromosomes pulled to opp poles of cell
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12
Q

Telophase II

A

-spindle fibres disintegrate and nuclear envelopes form

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13
Q

Cytokinesis II

A
  • cells divide, form 4 daughter cells (each haploid)
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14
Q

Importance of meiosis in sexual reproduction

A
  • gives genetic variation (crossing over during prophase I, independent assortment at metaphase I, random seperation of homologous chromosomes at anaphase I)
  • fertilisation is random, result in variation
  • variation increases chances of survival of species when there are environmental changes
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15
Q

Differences between mitosis and meiosis (MITOSIS)

A
  • occur in all cells
  • function: growth, repair
  • 1 nuclear division, produce 2 diploid cells, same no. of chromosomes as parent
  • daughter cells genetically identical to parent cell
  • homologous chromosomes dont pair up at prophase, no crossing over
  • line up singly (M)
  • sis chromatid separate, centromeres divide (A)
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16
Q

Differences between mitosis and meiosis (MEIOSIS)

A
  • occur only in reproductive organs
  • function: produce gametes
  • 2 nuclear divisions, 4 haploid daughter cells (half no. of chromosomes)
  • daughter cells are genetically diff (genetic variation)
  • homologous chromosomes pair up, crossing over may occur at prophase I
  • bivalent line up (M I)
  • centromeres don’t divide, homologous chromosomes separated (A I)