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BB10005 > Meiosis > Flashcards

Meiosis Flashcards

1
Q

goal of meiosis

A

Produce haploid cells with genetic material for sexual reproduction

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2
Q

diploid

A

two copies of every chromosome maternal and paternal 2n

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3
Q

Haploid

A

one copy of each chromosome 1n

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4
Q

Meiosis is

A

cell division with 2 rounds of chromosome segregation

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5
Q

Meiosis is after

A

dna replication

2n- 4n

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6
Q

Meiosis 1

A

segregate homologous chromosomes

4n-2n

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7
Q

Meiosis 2

A

segregate sister chromatids

2n-1n

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8
Q

Genetic diversity in meiosis

A

Mix up paternal and maternal dna: homologous recomb
Shuffle maternal and paternal sets of chromosomes
All Mixing occurs in first round

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9
Q

Mitosis review

A

See mitosis review diagram

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10
Q

Meosis 1 vs mitosis

A

1 vs 2 stages
Meiosis 1 is the most different from mitosis

Main difference is that in prophase there is pairing of the maternal and paternal chromsomes (homologous pair)
In anaphase these move to opposite poles of the cell

SIster chromatids (each set) have only 1 kinetochore compared to in mitosis, where they have 2

In anaphase 1 sister chromatids stay together
Instead homologous pairs move apart

Telophase 1 no cytokinesis

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11
Q

When is homologous recomb?

A

prophase

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12
Q

Meiosis II

A

no further dna repl, goes straight into metaphase 2

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13
Q

Meiosis I stages

A

interphase, prophase, metaphase 1, Anaphase 1, Telophase 1 (2 new nuclei formed- not new cells)

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14
Q

Meiosis 2 stages

A

Metaphase 2, Anaphase 2, Telophase 2, Cytokinesis

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15
Q

Prophase I: five stages

A 
Leptotene,
 Zygotene
Pachytene
Diplotene
Diakinesis
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16
Q

Zygotene

A

Homologous chromosomes pair up

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17
Q

Pachytene

A

Pairing complete

Homologous chromosomes begin to exchange genetic material in homologous recomb

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18
Q

Diplotene

A

Pairing becomes less tight, sister chromatid pairs are visible
See evidence of crossing over

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19
Q

Diplotene

A

Pairing between homo chromosomes becomes less tight, sister chromatid pairs are visible
See evidence of crossing over

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20
Q

Diakinesis

A

Chromatid pairs begin to separate

nuclear envelope breaks down, spindle begins to form

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21
Q

Homologous chromosome pairing

A

Pair via complementary DNA sequences

Line up at the metaphase plate independently and become paired there

22
Q

What do the 2 pairs of sister chromatids form and what are they joined by

A

Form a four chromosome bivalent

Joined by synaptonemal complex (proteins)

23
Q

What is the process of pair of sister chromatids joining called

A

synapsis

- at this point the chromosome pairs can swap material

24
Q

Heteroduplexes

A

DNA double helix composed of strands that originate from 2 different duplexes (helixes)
Rapid zippering when complementary sequences meet

25
Q

Synaptonemal complexes are tripartite

A

3 elements:
cohesins, axial cores and transverse fibres
see useful diagram
chromatid-cohesin-axial core- transverse filament- axial core-cohesin- chromatid

26
Q

How do the homologous strands find each other?

A

rare
unless double stranded break- both threads of dna double helix severed

Meiosis 1 induces programmed double strand breaks to allow homologous recomb

27
Q

Repair of broken dna using

A

Homologous chromosome as a template
- adv of having 2 sets of each chromosome
Often occurs after dna repl in mitosis (lots of double stranded breaks)
eg if something happens to maternal chromosome 2, you have paternal chromosome 2 as a template

28
Q

Meiosis specific double strand break repair process

A

Nucleases induce DSBs (double strand breaks)

Favour the maternal-paternal heteroduplexes ( over normal sister chromatids eg maternal-maternal)

29
Q

How does double strand break repair work

A
  1. Broken end processing:
    - nucelases chew broken ends to leave ssDNA overhangs
  2. Strand exchange:
    - protein complex binds the ssDNA and a double helix, which pulls it apart
    - if sequences match, pairing of different strands can occur
    see useful diagram
  3. DNA synthesis to fill in gaps
  4. Cut and ligate repaired strands
30
Q

Junctions where dna crosses over each other and is cut

A

Holliday junction

31
Q

Crossed over dna is in what configuration

A

open

32
Q

When you cut at holiday junctions you get

A

crossover or conversion

33
Q

Chiasma (crossover)

A

crossing, intersection

Bridges at crossover points

34
Q

What do cells ensure with crossovers

A

That they don’t happen too near each other

Would destabilise chromosome and incr chance of unfavourable deletion, translocation etc

35
Q

Gene conversion

A

Bit of maternal strand copied into paternal, or vice versa
May be some mismatched bases due to differences in DNA sequence
The cell will fix this later on in its cell cycle: mismatch repair- 50 % chance of choosing either strand?

36
Q

Metaphase 1

A

kinetochores in homologous pairs are monooriented - pointing in same direction

37
Q

Prophase 1

A

synaptonemal complex is degraded- digest between homologous pairs
Chromosomes only linked by crossover points

38
Q

Cohesins near kinetochores protected from what in meiosis

A

separase which cuts through cohesins

In anaphase 1 you get cleavage of all cohesins except ones near kinetochores

39
Q

Anaphase 1

A

Microtubules pull homologous pair away from each other, crossover points break

40
Q

Metaphase II

A

reorientation of kinetochores: become bioriented, pointing in opposite directions
Instead of being fused in a pair of chromatids, they break apart and go with the sister chromatids to each pole

41
Q

Reorinentation of kinetochores from metaphase I to II involves

A

Cohesin depletion of cohesin holding chromatids together (by separase)
Pulling force from microtubules in anaphase II

42
Q

Cohesin cleavage in meiosis II

A

special versions of cohesin are used in meiosis- slightly different to mitosis cohesin

Cohesin protected near centromere by binding to Sgo1 in meiosis 1

43
Q

Sgo is a target of what and when

A

APC
meiosis II
to allow sister chromatids to be pulled apart

44
Q

What is Sgo1 also involved in

A

sensing tension at kinetochores

45
Q

independent assortment gives

A

2^n possible combos

46
Q

Crossing over

A

swap large segments of homologous chromosomes- get unique combos

47
Q

gene conversion

A

non-crossing over homologous recomb

Mis-match repair may copy maternal sequence into paternal chromosome, or vice versa

48
Q

Non disjunction

A

chromosome segregation goes wrong

eg down syndrome

49
Q

Spermatogenesis

A

formation of sperm cells

spermatogonium under goes meiosis to form 4 haploid sperm

50
Q

oogenesis

A

oocyte forming egg cells
one haploid egg cell formed per meiosis
Half the chromosomes disposed of in polar bodies in metaphase 1 and 2
OOcyte meiosis arrests in metaphase II util fertilisation

BB10005 (27 decks)

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