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Cell Biology > Meiosis > Flashcards

Meiosis Flashcards

1
Q

What are the stages and substages of meiosis?

A

1) Interphase
2) (Meiosis 1)
3) Prophase 1
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakenesis
4) Metaphase 1
5) Anaphase 1
6) Telophase 1
7) Interphase 1
8) (Meiosis 2)
9) Prophase 2
10) Metaphase 2
11) Anaphase 2
12) Telophase 2

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2
Q

What happens in interphase?

A

The cell is carrying out
its normal activities. It is
not clear if the cell is in
G1, S-phase or G2.

Cells in S-phase are
replicating their DNA

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3
Q

Interphase is the […] stage

A

Interphase is the longest stage

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4
Q

Interphase has 3 stages:

A

G1, S, G2

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5
Q

What is G1 phase?

A
  • housekeeping
  • before S phase each chromosome is present as one DNA molecule (chromatid).
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6
Q

What is S phase?

A
  • synthesis of DNA
  • after S phase each chromosome is present as two DNA molecules
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7
Q

What is G2 phase?

A
  • preparation for cell division
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8
Q

Substages of prophase 1?

A

Leptotene
Zygotene
Pachytene
Diplotene
Diakenesis

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9
Q

What happens in prophase 1?

A
  • Zygotene
  • Pairing takes place between homologous chromosomes.
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10
Q

What does Homologous Chromosomes mean?

A
  • This term means ‘the same’
  • Here it refers to chromosomes that generally have the same genes and similar DNA sequences but these DNA sequences are not identical.
  • In the case of human chromosomes each ‘pair’ of chromosomes is homologous e.g. the two chromosome 21’s
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11
Q

In prophase 1, a protein structure synaptonemal complex) forms between …

A

…the homologous chromosomes holding them together

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12
Q

In prophase 1, the pairing begins at …

A

…a few sites along the chromosomes and brings corresponding parts together

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13
Q

Describe Prophase 1 Pachytene

A

The homologous chromosomes are fully paired and contracted

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14
Q

Whats the name of the protein structure which forms in prophase 1 between the homologous chromosomes holding them together?

A

synaptonemal complex

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15
Q

What occurs in pachytene?

A
  • Crossing over / recombination occurs.
  • For each crossing over event the DNA breaks in each of two non- sister chromatids followed by crosswise rejoining of the broken ends.
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16
Q

Define Chiasmata

A
  • Sites of crossing over, occur in synapsis.
  • Exchange of genetic material between non-sister chromatids.
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17
Q

Crossing over produces…

A

… recombinant chromosomes.

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18
Q

What happens in Diplotene?

A
  • The synaptonemal complex breaks down
  • The homologous chromosomes are held together by the crossovers.
  • (Each chromosome at this stage comprises two sister chromatids)
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19
Q

What happens in Chiasma?

A
  • The homologous chromosomes now ‘repel’ each other and reorganise themselves in three dimensional space.
  • The result is often a cross shape called a chiasma
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20
Q

There is at least one and usually more crossovers for …

A

…‘pair’ of homologous chromosomes

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21
Q

Crossovers have two roles:

A
  • to hold the homologous chromosomes together after the synaptonemal complex has broken down; this ensures that the homologous chromosomes separate into the new cells correctly (segregate)
  • to generate new arrangements of DNA (genetic variation)
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22
Q

Homologous chromosomes usually carry the same gene but …

A

…different versions (alleles) e.g. A and a

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23
Q

After crossovers, the different alleles in homologous chromosomes are …

A

…physically recombined into new orders

  • Resulting in genetic variation
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24
Q

What happens in Diakinesis?

A
  • The chromosome ‘pairs’ continue to condense
  • If the chromosomes are held as a pair they are called bivalents
  • If the chromosomes are held in threes they are called a trivalent.
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25
Q

What happens in Metaphase 1?

A

1) The chromosome ‘pair’ is attached to the spindle fibres by their centromeres
2) The chromosome ‘pairs’ move towards the equator

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26
Q

How many chromosomes and chromatids does a bivalent have?

A
  • 2 chromosomes
  • 4 chromatids
27
Q

In Metaphase, the centromeres line up in the…

A

…centre of the cell (the equator)

28
Q

What happens in anaphase 1?

A
  • The attraction between the sister chromatids lapses.
  • The chromosomes move apart to opposite poles
  • At this stage in a diploid organism each new cell becomes haploid
29
Q

What happens in Telophase 1?

A
  • The chromosomes relax and become long and thin again
  • In some species a cell wall forms between the two products (sometimes called interkinesis)
  • These two cells now progress through the rest of meiosis independently, though often in synchrony
30
Q

The interphase stage does not usually occur in the…

A

…middle of meiosis

31
Q

Where there is an interphase …

A

…no DNA replication occurs (no S Phase)

32
Q

There is no […] phase in meiosis when there is an […]

A

There is no S phase in meiosis when there is an interphase.

33
Q

What would the outcome from Meiosis be if the organism was tetraploid?

A

4 diploid cells

34
Q

WHat happens in prophase 2

A
  • Early prophase 2 looks similar to prophase 1
  • But each visible structure is one chromosome
35
Q

What happens in Metaphase 2?

A

Each chromosome attaches to the spindle by its centromere and is drawn to the equator.

36
Q

How many chromosomes and chromatids in metaphase 2?

A

One chromosome, two chromatids

37
Q

What happens in anaphase 2?

A

The chromatids separate and move to opposite poles

38
Q

How many chromatids in anaphase 2?

A

One chromatid

39
Q

What happens in telophase 2?

A
  • Four new cells with nuclear membranes form
  • Each cell usually has half the original number of chromosomes
40
Q

Outcome from Meiosis?

A
  • Four cells (compared to two in mitosis)
  • Not genetically identical: each crossover results in two recombined chromatids
41
Q

What would happen if the organism was triploid? (three copies of each chromosome)

A

The chromosome number may be halved

42
Q

in triploids (3x), pentaploids (5x) etc. …

A

…aberrations (e.g. non disjunction) are common.

43
Q

During normal cell growth, mitosis produces …

A

…daughter cells identical to parent cell (2n to 2n)

44
Q

Meiosis results in…

A

…genetic variation

45
Q

Meiosis results in genetic variation …

A

…by shuffling of maternal and paternal chromosomes and crossing over.

46
Q

No daughter cells formed during meiosis are …

A

…genetically identical to either mother or father

47
Q

During sexual reproduction, fusion of the unique haploid gametes produces …

A

…truly unique offspring.

48
Q

How many possible combination in independent assortment?

A

4 possible combinations

49
Q

How many possible combinations in haploid humans?

A

8 million possible combinations!

50
Q

64 trillion combinations for …

A

…a diploid zygote!!!

51
Q

When does dna replication occur in mitosis?

A

Occurs during interphase before nuclear division begins

52
Q

When does dna relplication in meiosis occur?

A

Occurs once, during the interphase before meiosis I begins.

53
Q

Number of divisions in mitosis?

A

One, including prophase, metaphase, anaphase, and telophase

54
Q

Number of divisions in meiosis?

A

Two, each including prophase, metaphase, anaphase, and telophase.

55
Q

Synapsis of homologous chromosomes in mitosis?

A

Does not occur

56
Q

Synapsis of homologous chromosomes in meiosis?

A

Synapsis is unique to meiosis: During prophase 1, the homologues chromosomes join along their length, forming tetrads (groups of four chromatids)l synapsis is associated with crossing over between non sister chromatids.

57
Q

Number of daughter cells and genetic compostion of mitosis?

A

Two, each diploid (2n) and genetically identical to the parent cell.

58
Q

Number of daughter cells and genetic composition of meiosis?

A

Four, each haploid (n), containing half as many chromosomes as the parent cell, genetically non identical to the parent cell and to each other.

59
Q

Role of mitosis in the animal body?

A

Enables multicellular adult to arise from zygote; produces cells for growth and tissue repair

60
Q

Role of meiosis in the animal body.

A

Produces gametes; reduces chromosome number by half and introduces genetic variability among the gametes.

61
Q

Define life cycle

A

sequence of stages in organisms reproductive history; conception to reproduction.

62
Q

Define somatic cells

A

any cell other than gametes, most of the cells in the body.

63
Q

Gametes are produced by…

A

… meiosis

Cell Biology (19 decks)

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