Meiosis 6.3

Question 1

How many copies of each chromosome do we have in each cell?

Answer 1

We have two copies of each chromosome, one from both parents and our cells are called diploids.

Question 2

Sex cells

Answer 2

They are called gametes and must each have only one chromosome or children would have double the chromosomes that we actually have. They are called haploids.

Question 3

Meiosis

Answer 3

the formation of gametes that have half the chromosomes of a normal cell. Meiosis is known as reduction division

Question 4

How do our cells store chromosomes

Answer 4

In a cell, we have two chromosomes of each type called homologous chromosomes and within these, we also have two copies of each gene, one from each parent. Each type of gene will code for a specific characteristic.

Question 5

Alleles

Answer 5

These are different versions of the same gene. An example may be eye colour. The gene will be for the colour of your eyes, but the different alleles may be the gene for blue eyes and the gene for brown eyes.

Question 6

Meiosis 1

Answer 6

This is when a cell will be divided and each cell will only get one of the homologous chromosomes. This means it will only have one full set of genes so will be a haploid cell instead of a diploid

Question 7

Meiosis 2

Answer 7

This is when the two haploid cells with one chromosome inside will separate into 4 haploid cells that contain 1 chromatid in each one. This is now a zygote.

Question 8

Meiosis 1 - Prophase 1

Answer 8

The chromosomes will condense, the nuclear envelope disappears and the spindle fibres will assemble.
The chromosomes will also pair up into their homologous chromosomes which are bivalents. As they are moving through the cytoplasm, the chromosomes will entangle and exchange chunks of DNA, this is called crossing over. Crossing over doesn’t finish until Anaphase.

Question 9

What do you see in a microscope during meiosis 1 prophase?

Answer 9

Little chromosome shapes paired up in the middle of the cell.

Question 10

Meiosis 1 - Metaphase 1

Answer 10

The bivalents will now align on the metaphase plate, in the centre which is the same as mitosis. However, any one of the homologous chromosomes can face either direction, it is random which results in genetic variation. This is called independent assortment.

Question 11

What do you see in a microscope during meiosis 1 metaphase

Answer 11

Bivalents all lined up along the centre which should be slightly longer than in mitosis.

Question 12

Meiosis 1 - Anaphase 1

Answer 12

The homologous chromosomes are being pulled to opposite ends of the cell, they stay joint to each other but the chromatids that became entangled during prophase will break off at the chiasmata and rejoin which means some DNA is exchanged between the two chromatids in each of the chromosomes. This results in genetic variation which forms recombinant chromatids as they could now have exchanged alleles. The sister chromatids are no longer identical.

Question 13

What do you see in a microscope during meiosis 1 anaphase?

Answer 13

The little v shapes being moved to either end of the cell.

Question 14

Meiosis 1 - Telophase 1

Answer 14

Each chromosome has now moved to either end of the cell and unwinded. The nuclear membrane has reformed and the cell undergoes cytokenesis into two haploid cells that contain 1 chromosome in it

Question 15

What do you see in a microscope during meiosis 1 telophase?

Answer 15

Two big masses at either end of the cell and a line forming through them.

Question 16

Meiosis 2 - Prophase 2

Answer 16

Now each of the chromosomes will condense again and become visible in the middle, the nuclear membrane will disappear and spindle fibres will be assembled etc…

Question 17

What do you see in a microscope during meiosis 2 prophase

Answer 17

You’ll see big masses in both the cells.

Question 18

Meiosis 2 - Metaphase 2

Answer 18

The chromosomes will assemble on the metaphase plate and will cross over again which results in further genetic variation as they still exchange DNA. More independent assortment

Question 19

What do you see in a microscope during meiosis 2 metaphase

Answer 19

The chromosomes assembled and crossing over in the middle.

Question 20

Meiosis 2 - Anaphase 2

Answer 20

This is the same as the anaphase in mitosis, each of the chromatids will be pulled to either end of the cell by shortening spindle fibres, but again each one will be genetically varied.

Question 21

What do you see in a microscope during meiosis 2 anaphase?

Answer 21

Lines being pulled to either end of the cell

Question 22

Meiosis 2 - Telophase 2

Answer 22

The chromatids are now at both ends of the cell and will unwind into chromatin. The nuclear membrane will form and the nucleolus. Cytokinesis will then occur to produce 4 genetically different daughter haploid cells which are used as gametes.

Question 23

What do you see in a microscope during meiosis 2 telophase?

Answer 23

4 cells with nuclei being pinched off.

Question 24

What causes genetic variation in cell division?

Answer 24

Metaphase 1 - the chromosomes could be facing either orientation. This is independent assortment
Anaphase 1 - the chromosomes are pulled apart but the regions that were crossed over will break off at the chiasmata and rejoin which will exchange DNA between the 2 chromosomes, leaving each one genetically different and forming recombinant alleles.
Metaphase 2 - the chromosomes are lined up on the metaphase plate and will cross over again which will lead to more variation.
Mutation - there could be wrong replication of DNA which hasn’t been detected by the checkpoints.
Non-disjunction - The bivalent might not have split during anaphase.