52. MEIOSIS I Flashcards

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1
Q
  1. How does Meiosis produce Haploid Cells from Diploid Cells?
A
  • the production of gametes
  • these are egg and sperm cells
  • the chromosome number is reduced by a half
  • each new cell has only 1 chromosome from each pair
    of homologous chromosomes
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2
Q
  1. What are the products of Meiosis?
A
  • 4 haploid cells
  • there is a pairing of homologous chromosomes
  • this is followed by 2 consecutive Meiotic Divisions
  • these divisions come from an initial diploid cell
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3
Q
  1. What follows after the Chromosomes duplicate?
A
  • two divisions follow:
  • Meiosis I (Reductional Division)
  • Meiosis II (Equational Division)
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4
Q
  1. What is Meiosis I?
A
  • the pairing and the separation of Homologous
    Chromosomes
  • this results in 2 haploid daughter cells
  • each of these cells have replicated chromosomes
  • 2 chromatids per chromosome
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5
Q
  1. What is Meiosis II?
A
  • it is when the sister chromatids separate
  • this results in 4 Haploid Daughter Cells
  • each of these has unreplicated chromosomes
  • there is 1 chromatid per chromosome
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6
Q
  1. Why does Meiosis I result in 2 haploid daughter cells?
A
  • the cells are haploid in terms of their chromosome
    content
  • they have one chromosome from each pair of
    homologs

THE DAUGHTER CELLS ARE DIPLOID (2n):
- in terms of DNA content (chromatids)
- these have replicated
- there are now 2 chromatids per chromosome

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7
Q
  1. What can be said about the number of chromosomes in human cells after Meiosis I?
A
  • human cells have 23 chromosomes
  • each has 2 chromatids
  • there are 46 chromatids in total (2n)

NUMBER OF CHROMOSOMES:
- n
- 23 in humans

NUMBER OF CHROMATIDS:
- 2n
- 46 in humans
- this is the DNA content

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8
Q
  1. Why does Meiosis II result in four haploid daughter cells?
A
  • the cells are haploid in terms of chromosome number
  • the cells are haploid in terms of DNA content
  • the cells are haploid in terms of Chromatid number
  • each chromosome has only 1 chromatid each

NUMBER OF CHROMOSOMES:
- n
- 23 chromosomes in humans

NUMBER OF CHROMATIDS:
- n
- 23 in humans
- this is the DNA content

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9
Q
  1. Which phase precedes Meiosis I?
A
  • Interphase
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10
Q
  1. What happens during Interphase?
A
  • DNA replication
  • the chromosomes duplicate to form sister chromatids
  • the sister chromatids are genetically identical
  • they have the same alleles and the same gene
    sequence
  • they are joined at the centromere
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11
Q
  1. What is a Centromere?
A
  • the region of a chromosome to which the microtubules
    of the spindle attach
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12
Q
  1. What happens to the single Centrosome during Interphase?
A
  • the centrosome replicates during Interphase
  • this forms two centrosomes
  • these replicate during the S-Phase
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13
Q
  1. What 5 phases does the division in Meiosis I occur in?
A
  1. Prophase I
  2. Metaphase I
  3. Anaphase I
  4. Telophase I
  5. Cytokinesis
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14
Q
  1. How long does Prophase I take?
A
  • it takes 90% of the time required for Meiosis
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15
Q
  1. What happens during Prophase I?
A
  • the chromosomes begin to condense
  • a synapsis happens
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16
Q
  1. What is a Synapsis?
A
  • it is the pairing of homologous chromosomes
  • they are aligned gene by gene
17
Q
  1. What happens after the Synapsis in Prophase I?
A
  • each pair of chromosomes forms a tetrad
  • a tetrad is a group of 4 chromosomes
  • this is also known as a Synaptonemal Complex
18
Q
  1. What is present in each Tetrad?
A
  • each tetrad usually has one or more chiasmata
  • these are the X-Shaped regions where crossing over
    occurs
19
Q
  1. What is Genetic Recombination (Crossing Over)?
A
  • it is the exchange of DNA segments
  • these are exchanged between non-sister chromatids of
    Homologous Chromosomes
  • this may or may not occur during Prophase I in Meiosis I
  • it is a random event
  • it has an effect on variation if it does happen
20
Q
  1. What happens during Metaphase I?
A
  • the tetrads line up at the Metaphase plate
  • each Homologous chromosome faces each pole

MICROTUBULES FROM ONE POLE:
- are attached to the kinetochore of one chromosome
from each tetrad

MICROTUBULES FROM THE OTHER POLE:
- are attached to the Kinetochore of the other
chromosome

21
Q
  1. What happens during Anaphase I?
A
  • the homologous chromosome pairs separate
  • each homologous chromosome moves towards the
    opposite pole

THE SISTER CHROMATIDS REMAIN ATTACHED:
- at the centromere
- these chromatids are duplicated
- they move as one unit towards the pole

22
Q
  1. What happens during Telophase I?
A
  • each half cell has a haploid set of chromosomes
  • each chromosome still consists of two sister
    chromatids
23
Q
  1. What is the last stage of Meiosis I?
A
  • Cytokinesis
24
Q
  1. What is Cytokinesis?
A
  • it is the cytoplasm division
  • it allows for the formation of 2 haploid daughter cells
25
Q
  1. How does Cytokinesis happen in animal cells?
A
  • a cleavage furrow forms
26
Q
  1. How does Cytokinesis happen in plant cells?
A
  • a cell plate forms