Meiosis

Question 1

What is meiosis?

Answer 1

It produces haploid cells with genetic material for sexual reproduction.

Question 2

What does diploid mean?

Answer 2

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

Question 3

What does haploid mean?

Answer 3

One copy of each chromosome.

Question 4

What is a gamete?

Answer 4

A sperm or egg cell.

Question 5

What is a zygote?

Answer 5

When two gametes fuse.

Question 6

What happens in meiosis 1?

Answer 6

The homologous chromosomes segregate.

Question 7

What happens in meiosis 2?

Answer 7

The sister chromatids segregate.

Question 8

What is homologous recombination?

Answer 8

When the maternal and paternal DNA mixes up.

Question 9

When does homologous recombination occur?

Answer 9

In the first round of meiosis.

Question 10

What are the phases in meiosis 1?

Answer 10

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

Question 11

What happens in meiosis 2?

Answer 11

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

Question 12

What are the stages in prophase 1?

Answer 12

Leptotene, zygotene, pachytene, diplotene and diakinesis.

Question 13

What happens in leptotene?

Answer 13

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

Question 14

What happens in zygotene?

Answer 14

When homologous chromosomes pair up.

Question 15

What happens in pachytene?

Answer 15

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

Question 16

What happens in diplotene?

Answer 16

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

Question 17

What happens in diakinesis?

Answer 17

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

Question 18

How do chromosomes pair?

Answer 18

Via complementary DNA sequences.

Question 19

What is synapsis?

Answer 19

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

Question 20

What is a synaptonemal complex?

Answer 20

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

Question 21

What are the three elements of synaptonemal complexes?

Answer 21

Cohesins, axial core and transverse fibers.

Question 22

What are heteroduplexes?

Answer 22

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

Question 23

How do homologous strands find eachother?

Answer 23

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

Question 24

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

Answer 24

For recombination.

Question 25

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

Answer 25

Broken DNA can be repaired.

Question 26

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

Answer 26

Maternal-paternal chromosome heteroduplexes.

Question 27

What is the first step in double strand break repair?

Answer 27

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

Question 28

What is the second step in double strand break repair?

Answer 28

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.

Question 29

What is the third step in double strand break repair?

Answer 29

DNA synthesis to fill in the gaps.

Question 30

What is the fourth step in DNA strand break repair?

Answer 30

Cut and ligate the repaired strands.

Question 31

What is holiday junction?

Answer 31

A cross-shaped structure that forms during recombination.

Question 32

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

Answer 32

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

Question 33

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

Answer 33

Crossover.

Question 34

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

Answer 34

Conversion.

Question 35

What are chiasmata?

Answer 35

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

Question 36

How often does crossing over occur?

Answer 36

10% of the time.

Question 37

How many crossing overs are there per chromosome?

Answer 37

At least one.

Question 38

What is gene conversion?

Answer 38

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).

Question 39

When are sister chromatid kinetochores fused?

Answer 39

Meiosis 1.

Question 40

When is the synaptonemal complex degraded?

Answer 40

Prophase 1.

Question 41

What are cohesins near kinetochores protected by in meiosis 1?

Answer 41

Separase.

Question 42

When do sister chromatid pairs move to poles?

Answer 42

Anaphase 1.

Question 43

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

Answer 43

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

Question 44

What is Sgo1?

Answer 44

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

Question 45

What factors play into genetic diversification?

Answer 45

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

Question 46

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

Answer 46

2^23.

Question 47

What is crossing over?

Answer 47

Swapping large segments of homologous chromosomes.

Question 48

What is gene conversion?

Answer 48

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

Question 49

What is non-disconjunction?

Answer 49

When chromosome segregation goes wrong.

Question 50

What are some conditions in which non-disconjunction occurs?

Answer 50

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

Question 51

How many haploid sperm are produced per meiosis?

Answer 51

4.

Question 52

How many egg cells are produced per meiosis?

Answer 52

1.