Meiosis

Question 1

What is the importance of meiosis?

Answer 1

• it ensures all daughters cells have a chromosal number of 23 so during sexual reproduction, the diploid number of 46 is maintained
• Meiosis also produces genetic variation: crossing over and independent assortment

Question 2

What happens in prophase 1

Answer 2

• the nuclear membrane breaks down and chromosomes condense
• spindle is formed and centrioles move to opposite poles
• homologous chromosomes pair up and form bivalents
• crossing over occurs between non sister chromatids
• these crossing points are called chiasmatas

Question 3

What happens in metaphase 1

Answer 3

• the bivalents line up in the centre of the cell along the equator of the spindle
• spindle fibres attach to centromeres

Question 4

What happens in anaphase 1

Answer 4

• spindle fibres contract and pull the each set of chromosomes to opposite poles
• the centromeres do not divide

Question 5

What happens in telophase 1

Answer 5

• Each set of chromosomes arrive at opposite poles
• the nuclear membrane forms around each set of chromosomes

Question 6

What does not happen between meiosis 1 and 2

Answer 6

• Interphase does not occur so chromosomes are not replicated

Question 7

What happens in prophase 2

Answer 7

• the nuclear membrane breaks down and chromosomes condense
• spindles form at right angles to the old ones

Question 8

What happens in metaphase 2

Answer 8

• Chromosomes line up in the equator of a cell and spindle fibres attach to the centromeres

Question 9

What happens in anaphase 2

Answer 9

• The spindle fibres contract and the centromeres divide
• chromatids are pulled to opposite poles, forming four groups of chromosomes with the half the number as parent cells

Question 10

What happens in telophase 2

Answer 10

• Nuclear membranes form around each group of chromosomes (4)

Question 11

What happens in cytokenisis?

Answer 11

• The cytoplasm divides forming four haploid daughter cells

Question 12

What two ways does meiosis produce genetic variation

Answer 12

• crossing over
• independent segregation

Question 13

What is crossing over?

Answer 13

• non - sister chromatids exchange alleles
• non sister chromatids cross over and become twisted around each other and become twist around each other
• these crossing over points are called chiasmata
• the crossing over produces stress and tensions and this results in sections of chromosomes breaking and rejoining on their homologous partner
• this produces new combinations of alleles and creates genetic variation

Question 14

What is independent assortment?

Answer 14

In prophase 1, homologous chromosomes pair up and from bivalents.
However, in metaphase, these chromosomes are pulled to different poles of the spindle
This creates different combinations of alleles in daughter cells and creates genetic variation

Question 15

How many combinations of chromosomes are there in diploid cells

Answer 15

2 to the power of 23 = 8,388,608 in one gamete

Question 16

What is the equation for this?

Answer 16

2 to the power of n where n is the number of chromosomes divided by 2