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BB10005 > Meiosis > Flashcards

Meiosis Flashcards

1
Q

What is meiosis?

A

It produces haploid cells with genetic material for sexual reproduction.

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2
Q

What does diploid mean?

A

There are two copies of every chromosome, maternal and paternal.

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3
Q

What does haploid mean?

A

One copy of each chromosome.

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4
Q

What is a gamete?

A

A sperm or egg cell.

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5
Q

What is a zygote?

A

When two gametes fuse.

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6
Q

What happens in meiosis 1?

A

The homologous chromosomes segregate.

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7
Q

What happens in meiosis 2?

A

The sister chromatids segregate.

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8
Q

What is homologous recombination?

A

When the maternal and paternal DNA mixes up.

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9
Q

When does homologous recombination occur?

A

In the first round of meiosis.

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10
Q

What are the phases in meiosis 1?

A

Interphase, prophase, metaphase 1, anaphase 1 and telophase 1.

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11
Q

What happens in meiosis 2?

A

Interphase 2, metaphase 2, anaphase 2, telophase 2 and cytokinesis.

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12
Q

What are the stages in prophase 1?

A

Leptotene, zygotene, pachytene, diplotene and diakinesis.

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13
Q

What happens in leptotene?

A

There is condensation of sister chromatids - they look like thin threads.

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14
Q

What happens in zygotene?

A

When homologous chromosomes pair up.

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15
Q

What happens in pachytene?

A

When pairing is complete and homologous chromosomes begin to exchange genetic material.

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16
Q

What happens in diplotene?

A

When pairing becomes less tight and sister chromatid pairs are visible and there is evidence of crossing over.

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17
Q

What happens in diakinesis?

A

The chromatid pairs begin to separate and the nuclear envelope breaks down and spindle forms.

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18
Q

How do chromosomes pair?

A

Via complementary DNA sequences.

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19
Q

What is synapsis?

A

When two pairs of sister chromatids form a four-chromosome bivalent.

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20
Q

What is a synaptonemal complex?

A

When two pairs of sister chromatids form a four-chromosome bivalent.

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21
Q

What are the three elements of synaptonemal complexes?

A

Cohesins, axial core and transverse fibers.

22
Q

What are heteroduplexes?

A

DNA double helixes composed of strands that originate from the two different duplexes. There s rapid zippering when c

23
Q

How do homologous strands find eachother?

A

It is a rare event, unless double stranded break occurs.

24
Q

Why is there a programmed double strand break in meiosis i?

A

For recombination.

25
Q

What is an advantage of having two sets of each chromosome during meiosis?

A

Broken DNA can be repaired.

26
Q

What does the meiosis-specific double strand break repair process favour?

A

Maternal-paternal chromosome heteroduplexes.

27
Q

What is the first step in double strand break repair?

A

Broken end processing: Nucleases chew broken ends to leave single stranded DNA overhangs.

28
Q

What is the second step in double strand break repair?

A

Strand exchange: protein complexes bind the ssDNA and a double helix which it pulls apart. If the sequences match, pairing of different strands can occur.

29
Q

What is the third step in double strand break repair?

A

DNA synthesis to fill in the gaps.

30
Q

What is the fourth step in DNA strand break repair?

A

Cut and ligate the repaired strands.

31
Q

What is holiday junction?

A

A cross-shaped structure that forms during recombination.

32
Q

What are the two ways in which holiday junctions can be re-sealed?

A

Cut and re-seal along the V axis or cut and re-seal along the H axis. (horizontal or vertical).

33
Q

What is it called when the holiday junction is cut and resealed along the vertical axis?

A

Crossover.

34
Q

What is it called when the holiday junction is cut and resealed along the horizontal axis?

A

Conversion.

35
Q

What are chiasmata?

A

Where the strands of DNA cross and intersect during crossing over.

36
Q

How often does crossing over occur?

A

10% of the time.

37
Q

How many crossing overs are there per chromosome?

A

At least one.

38
Q

What is gene conversion?

A

When part of a maternal strand is copied into the paternal (or vice versa). There may be some mis-matched bases due to differences in the DNA sequences (cut along the horizontal axis).

39
Q

When are sister chromatid kinetochores fused?

A

Meiosis 1.

40
Q

When is the synaptonemal complex degraded?

A

Prophase 1.

41
Q

What are cohesins near kinetochores protected by in meiosis 1?

A

Separase.

42
Q

When do sister chromatid pairs move to poles?

A

Anaphase 1.

43
Q

What does the reorientation of kinetochores involved in metaphase 1 and 2?

A

Cohesin depletion and the pulling force from microtubules in metaphase 2.

44
Q

What is Sgo1?

A

A target of the APC in meiosis 2. It is also involved in sensing tension at kinetochores.

45
Q

What factors play into genetic diversification?

A

Independent assortment of maternal and paternal chromosomes, crossing over, gene conversion and non-disjunction.

46
Q

How many possible combinations of chromosomes are there for independent assortment?

A

2^23.

47
Q

What is crossing over?

A

Swapping large segments of homologous chromosomes.

48
Q

What is gene conversion?

A

Non-crossing over homologous recombination. Mis-match repair may copy maternal sequence into the paternal chromosome or vice versa.

49
Q

What is non-disconjunction?

A

When chromosome segregation goes wrong.

50
Q

What are some conditions in which non-disconjunction occurs?

A

Down syndrome, trisomy 28 or 13, turner syndrome, klinefelter syndrome or where there are XYY chromosomes present.

51
Q

How many haploid sperm are produced per meiosis?

A

4.

52
Q

How many egg cells are produced per meiosis?

A

1.

BB10005 (22 decks)

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