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MED 103- BIOLOGY I > 53. MEIOSIS II > Flashcards

53. MEIOSIS II Flashcards

1
Q
  1. What cannot occur between the end of Meiosis I and the beginning of Meiosis II?
A
  • there can be no chromosome replication
  • this is because the chromosomes are already
    replicated
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2
Q
  1. Which process is Meiosis II very similar to?
A
  • Mitosis
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3
Q
  1. What are the 5 phases of Meiosis II?
A
  1. Prophase II
  2. Metaphase II
  3. Anaphase II
  4. Telophase II
  5. Cytokinesis
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4
Q
  1. What happens during Prophase II?
A
  • it is when a spindle apparatus forms

IN LATE PROPHASE II:
- the chromosomes move towards the Metaphase Plate
- these chromosomes are still composed of two
chromatids

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5
Q
  1. What happens during Metaphase II?
A
  • the sister chromatids are arranged at the Metaphase
    Plate

IF CROSSING OVER HAS OCCURRED IN MEIOSIS I:
- the two sister chromatids of each chromosome may
no longer be genetically identical

THE KINETOCHORES OF THE SISTER CHROMATIDS:
- attach to the microtubules
- they extend from the opposite poles

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6
Q
  1. What happens during Anaphase II?
A
  • the sister chromatids separate
  • the sister chromatids of each chromosome now move
  • they move as two newly individual chromosomes
  • they move towards the opposite poles
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7
Q
  1. What happens during Telophase II?
A
  • the chromosomes arrive at the opposite poles
  • the nuclei reform
  • the chromosomes decondense
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8
Q
  1. What happens during Cytokinesis?
A
  • the cytoplasm divides
  • there are 4 daughter cells at the end of Meiosis
  • each has a haploid set of unreplicated chromosomes
  • there is 1 chromatid per chromosome
  • each daughter cell is genetically distinct from the
    others
  • each daughter cell is genetically distinct from the
    parental cell
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9
Q
  1. What is a vital difference between Mitosis and Meiosis?
A

MITOSIS:
- conserves the number of chromosome sets
- it produces cells that are genetically identical to the
parental cell
- they are also genetically identical to each other

MEIOSIS:
- reduces the number of chromosome sets
- it reduces them from diploid (2n) to haploid (n)
- it produces cells that are genetically different from
each other
- they are genetically different from the parental cell

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10
Q
  1. In humans, what kind of cells are produced by Mitosis?
A
  • 2 diploid cells
  • they are produced from 1 diploid cell
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11
Q
  1. In humans, what kinds of cells are produced by Meiosis?
A
  • 4 haploid cells
  • they are produced from 1 diploid cell
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12
Q
  1. What are the 3 events that are unique to Meiosis?
A

NB:
the following events only happen in Meiosis I

  1. SYNAPSIS AND CROSSING OVER:
    • this happens in Prophase I
  2. METAPHASE I:
    • the alignment of Homologous Chromosome Pairs
    • these are the Chromatid tetrads
    • these align instead of the individual replicated
      chromosomes
  3. ANAPHASE I:
    • the separation of the homologous chromosomes
    • instead of the sister chromatids
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13
Q
  1. Look at this image.
    Does everything make sense?
A
  • yes
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14
Q
  1. Look at this image.
    Does everything make sense?
A
  • yes
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15
Q
  1. Look at this image.
    Does everything make sense?
A
  • yes
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16
Q
  1. Look at this image.
    Does everything make sense?
A
  • yes
17
Q
  1. Look at this image.
    Does everything make sense?
A
  • yes
18
Q
  1. What contributes to Evolution?
A
  • sexual reproduction
  • this leads to genetic variation
19
Q
  1. What are the 4 mechanisms that contribute to Genetic Variation?
A
  1. INDEPENDENT ASSORTMENT OF CHROMOSOMES:
    • 2³³ combinations of homologous chromosomes in
      Meiosis
    • this produces 8 million gametes
  2. GENETIC RECOMBINATION:
    • crossing over
    • exchange of chromosomal segments
  3. RANDOM FERTILISATION:
    • there are more than 64 trillion possible offspring
  4. MUTATIONS:
    • create different version of the genes
    • these are called alleles
20
Q
  1. What is the Independent Assortment of Chromosomes?
A
  • homologous pairs of chromosomes orient randomly at Metaphase I of Meiosis I

IN INDEPENDENT ASSORTMENT:
- each pair of chromosomes sorts the maternal and the
paternal homologues into daughter cells
- it does this independently of the other pairs

21
Q
  1. How do we calculate the number of combinations possible when chromosomes assort themselves independently into gametes?
A
  • n = haploid number
22
Q
  1. Calculate how many possible gametes there are for humans?
A
  • n = 23
  • 2²³ = 8 388 608 gamete combinations for chromosomes
23
Q
  1. What does Crossing Over produce?
A
  • Recombinant chromosomes
  • these combine the DNA inherited from each parent
24
Q
  1. When does Crossing Over begin?
A
  • very early in Prophase I
  • it happens when the Homologous Chromosomes pair
    up gene by gene
  • this is known as Synapsis
25
Q
  1. What happens during Crossing Over?
A
  • the Homologous Portions of 2 non-sister chromatids
    exchange places
26
Q
  1. What does Crossing Over contribute towards?
A
  • genetic variation
  • it does this by combining DNA from the two parents
    into a single chromosome
27
Q
  1. How does Random Fertilisation add to Genetic Variation?
A
  • any sperm can fuse with an Ovum
  • this is the unfertilised egg
28
Q
  1. How many possible zygotes are there for human beings?
A

2²³ sperm cells x 2²³ egg cells = 70 trillion
∴ there are approximately 70 trillion possible zygotes

THIS MEANS THAT:
- the fusion of 2 gametes
- each with 8.4 million possible chromosome
combinations from independent assortment
- produce a zygote with any of about 70 trillion diploid
combinations

THIS IS WHAT MAKES US UNIQUE

29
Q
  1. What are Mutations?
A
  • they are the changes in an organism’s DNA
  • they are the original source of genetic diversity
  • they can be beneficial or harmful
  • or they can have no effect at all
30
Q
  1. What do Mutations create?
A
  • different versions of genes
  • these are called Alleles
31
Q
  1. What produces Genetic Variation?
A
  • the reshuffling of alleles
  • this happens during sexual reproduction
32
Q
  1. What is the Evolutionary Significance of Genetic Variation within Populations?
A
  1. SEXUAL REPRODUCTION
    • contributes to the genetic variation in a population
    • these variations originate from mutations
  2. NATURAL SELECTION
    • results in the accumulation of genetic variations
    • these are favoured by the environment
33
Q
  1. Read through Summary 1.
    Does everything make sense?
A
  • yes
34
Q
  1. Read through Summary 2.
    Does everything make sense?
A
  • yes
35
Q
  1. Read through Summary 3.
    Does everything make sense?
A
  • yes
36
Q
  1. Read through Summary 4.
    Does everything make sense?
A
  • yes
37
Q
  1. Read through Summary 5.
    Does everything make sense?
A
  • yes

MED 103- BIOLOGY I (53 decks)

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