2 - MZH - Meiosis

Question 1

Define meiosis

Answer 1

Form of cell division where the nucleus divides twice (meiosis 1 and meiosis 2) resulting in a halving of the chromosome number and producing 4 haploid cells from one diploid cell.

Question 2

State the 5 ways by which meiosis can create genetic variation?

Answer 2

• Crossing over in prophase 1
• Independant assortment in metaphase 1 (bivalents arrange themselves randomly)
• Independant assortment in metaphase 2
• Mutations
• Random fusion of gametes during fertilisation

Question 3

What happens in meiosis 1

Answer 3

First division - Reduction division

Pairs of homologous chromosomes are seperated in to 2 cells.

Each intermediate cell will only contain one full set of genes instead of two, so the cells are haploid.

Question 4

What happens in meiosis 2

Answer 4

Similar process to meiosis 1.

Pairs of daughter chromatids seperate into 2 cells. 4 haploid cells are produced.

Question 5

Purpose of the cells produced by meiosis being haploid?

Answer 5

Ensures that the chromosome number remains constant from one generation to the next.

Question 6

Interphase?

Answer 6

DNA of each chromosome replicated forming 2 identical chromatids hed together at the centromere.

Each cell now contins 4, rather than the original 2 copies of each chromosome.

Question 7

Prophase 1?

Answer 7

• Chromosomes cndense (shorten + fatten).
• Come together in their homologous pairs to form a bivalent (group of 4 chromatids).
• Chromatids wrap one another and attach at points called chiasmata.
• Crossing over takes place - produces genetic variation

Question 8

Metaphase 1?

Answer 8

• Independant assortment occurs (produces genetic variation)
• Centomeres attach themselves to the spndle fibires and the bivalents arrange themselves randomly at the equator (metaphase plate).

Question 9

Anaphase 1?

Answer 9

DIFFERENT TO ANAPHASE OF MITOSIS!

• One of each pair of homologous chromosomes is pulled by spindle fibres to opposite poles.
• Depending on how the chromosomes lined up on the equator different combinations of chromosomes will end up at the poles. (independant assortment)
• Sister chromatids are no longer identical.

Question 10

Telophase 1?

Answer 10

• Chromosomes assemble at each pole, nuclear membrane reforms, chromosomes uncoil.
• Cell undergoes cytokinesis and divides into 2 cells.
• Reduction of chromosome number from diploid to haploid is complete.

Cytoplasm divides and 2 cells are formed. These cells them immediately enter meiosis 2!

There is no interphase between meiosis 1 and meiosis 2.

Question 11

Which stage does not exist between meiosis 1 and meiosis 2?

Answer 11

Interphase

Question 12

Prophase 2?

Answer 12

No chiasmata is formed so no chrossing over occurs.

• Nuclear envelope breaks down, chromosomes condense and become visible.
• Spindle formation begins.

Question 13

Metaphase 2?

Answer 13

Independant assortment occurs - individual chromosomes assemble on the metaphase plate (randomly).

Question 14

Anaphase 2?

Answer 14

Chentromeres divide, daughter chromatids are pulled to opposite poles by the spindle fibres.

Question 15

Telophase 2?

Answer 15

• Nuclear envelope reforms again.
• Chromosomes uncoil and form chromatin again.
• Cytokinesis occurs and forms 4 daughter cells in total.
• Cells will be haploid due to the reduction division (meiosis 1).
• All 4 cells have a different genetic composition.

Question 16

What stage of mieosis is this?

Answer 16

Prophase 1

Question 17

What stage of mieosis is this?

Answer 17

Metaphase 1

Question 18

What stage of mieosis is this?

Answer 18

Anaphase 1

Question 19

What stage of mieosis is this?

Answer 19

Telophase 1

Question 20

What stage of mieosis is this?

Answer 20

Prophase 2

Question 21

What stage of mieosis is this?

Answer 21

Metaphase 2

Question 22

What stage of mieosis is this?

Answer 22

Anaphase 2

Question 23

What stage of mieosis is this?

Answer 23

Telophase 2