4.4 Meiosis

Question 1

What is meiosis?

Answer 1

A type of cell division that results in four genetically different daughter cells each with half the number of chromosomes of the parent cell (haploid).

Question 2

Meiosis results in the production of …

Answer 2

gametes.

Question 3

Why are daughter cell genetically different from one another and their parent cell?

Answer 3

• Independent Segregation
• Crossing Over

Question 4

What is independent segregation?

Answer 4

• it is random what side of the equator the paternal and maternal chromosomes from each homologous pair lie, so when the pairs are seperated, it is a random combination in each daughter cell
  -SO the combination of alleles that end up in each daughter cell depends on how the pairs of homologous chromosomes were lined up.

Question 5

What is crossing over?

Answer 5

1. chromatids of each homologous pair become twisted around each other
2. ** tension** created breaks off equal proportions of the chromatids
3. Broken parts rejoinw/ chromatids of its homologous partner
4. New genetic combinations are produced (alleles)

Question 6

How many divisions in meiosis?

Answer 6

2 divisions → Meiosis I and Meiosis II

Question 7

What happens before meiosis I?

Answer 7

Interphase

Question 8

What happens during prophase I?

Answer 8

• chromosomes condense
• Each chromosome consists of two sister chromatids joined together by a centromere
• The chromosomes are arranged side by side in homologous pairs(bivalent)
• Crossing over may occur (the point where they cross over is called a chiasma)
• Centrioles move to opposite poles and spindle fibres are formed
• The nuclear envelope breaks down and the nucleolus disintegrates

Question 9

What happens during metaphase I?

Answer 9

• The bivalents line up along the equator with the spindle fibres attached to the centromeres.

Question 10

What happens during anaphase I?

Answer 10

• spindle fibres contract
  -The homologous pairs of chromosomes are separated as centrioles pull whole chromosomes to opposite poles of the cell.

Question 11

What happens during telophase I?

Answer 11

• chromosomes decondense.
• Spindle fibres start to break down.
• Nuclear membrane reforms

Question 12

What are the products of cytokinesis after meiosis I?

Answer 12

Two haploid cells

Question 13

Describe meiosis II?

Answer 13

• There is no interphase before meiosis II
• The stages of meiosis II are almost identical to mitosis
• Produces four haploid daughter cells

Question 14

Name 3 sources of genetic variation (excluding independent segregation and crossing over).

Answer 14

• The different combinations of chromosomes following meiosis
• The different combinations of chromosomes following fertilisation
• The random fertilisation of gametes

Question 15

How many different combinations of chromosomes are there following meiosis?

Answer 15

2^{n
(where n is the number of homologous chromosome pairs)}

Question 16

How many different combinations of chromosomes are there following fertilisation?

Answer 16

(2ⁿ)^{2
(where n is the number of homologous chromosome pairs)}

Question 17

What does the random fertilisation of gametes mean?

Answer 17

Any two gametes may combine.
- each gamete carries substantially different alleles
- random fusion creates genetically diverse zygotes → genetic diversity within species

Question 18

what does meiosis form?

Answer 18

4 haploid daughter cells via cytokinesis II

Question 19

Meiosis Vs mitosis

Answer 19

MEIOSIS
- 2 nuclear divisions
- Haploid cell ( 1 set of chromosomes)
- Introduces genetic variation
- 4 daughter cells
- Different to parents
- crossing over
- homologous pairs separated

MITOSIS
-1 nuclear division
- Diploid cells (2 sets of chromosomes)
- genetically identical
- 2 daughter cells
- identical to parents
- NO crossing over
- do not get separated