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

the combination of alleles that end up in each daughter cell depends on how the pairs of homologous chromosomes were lined up).

The idea that the inheritance of one chromosome does not affect the inheritance of another chromosome (orientation of homologous pairs are random and are not influenced by the orientation of other pairs

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

• DNA condenses and becomes visible as chromosomes
• 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

• The homologous pairs of chromosomes are separated as centrioles pull whole chromosomes to opposite poles of the cell.
• The centromeres do not divide.

Question 11

What happens during telophase I?

Answer 11

• The chromosomes arrive at opposite poles.
• Spindle fibres start to break down.
• Nuclear envelopes form around the two groups of chromosomes and nucleoli reform.

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