Component 2.2 - Meiosis

Question 1

What is a bivalent?

Answer 1

The association of the two chromosomes of a homologous pair at prophase I of meiosis

Question 2

What is a chiasma?

Answer 2

The site at which the chromosomes exchange DNA in genetic crossing over

Question 3

What happens in late prophase 1 ?

Answer 3

1) chromosomes coil up and become shorter and thicker
2) centrioles separate and move to poles of cell
3) chromatids associate in pairs and wrap round each other at chiasma
4) segment of DNA exchanged
5) nuclear envelops disintegrates

Question 4

What happens in metaphase 1?

Answer 4

1) Pairs of homologous chromosomes align at the equator randomly
2) Each chromosome faces opposite pole
3) Independent assortment - random combination of chromosomes from each parent.

Question 5

What happens in anaphase 1?

Answer 5

1) chromosomes from each bivalent split
2) spindle fibres shorten pulling one of the pair to each pole
3) each pole gets a random combination of maternal and paternal

Question 6

What happens in early telophase 1?

Answer 6

Sometimes nuclear envelope reforms around haploid group of chromosomes and the chromosomes decondense but sometimes the chromosomes stay in condensed form

Question 7

What happens in late prophase 2?

Answer 7

The centrioles separate and organise a new spindle at right angles to the old spindle

Question 8

What happens in metaprophase 2 ?

Answer 8

1) Chromosomes line up along the equator and spindle fibres attach to each centromere
2) independent assortment happens

Question 9

What happens in anaprophase 2?

Answer 9

Centromeres divide and the spindle fibres shorten pulling chromatids to opposite poles

Question 10

What happens in early telophase 2?

Answer 10

Chromosomes reach the poles

Question 11

What happens in late telophase 2?

Answer 11

1) Chromatids lengthen and can no longer be distinguished

2) Nuclear envelope and nucleolus should reforms

Question 12

What provides genetic variation in meiosis ?

Answer 12

Crossing over

Independent assortment of chromosomes in metaphase 1 and different combination of chromatids in metaphase 2

Question 13

Why is variation important?

Answer 13

It produces selection pressures - evolution is based on it

To survive variation is essential

Question 14

What’s the difference in prophase in meiosis 1 and 2?

Answer 14

In meiosis 1 it follows DNA replication and crossing over takes place but this does not happen on meiosis 2

Question 15

What’s the difference in metaphase in meiosis 1 and 2?

Answer 15

In meiosis 1 the homologous pairs align either side of the equator whereas in meiosis 2 the chromosomes align on the equator

In meiosis 1 it is independent assortment of homologous chromosomes and in meiosis 2 it is independent assortment of chromatids

Question 16

What’s the difference in anaphase in meiosis 1 and 2?

Answer 16

In meiosis 1 chromosomes are separated but in meiosis 2 chromatids are separated

Number of daughter cells from meiosis 1 is 2 but 4 in meiosis 2

Question 17

What does meiosis form?

Answer 17

Four genetically distinct haploid gametes