9.2: Meiosis and genetic variation

Question 1

What does Mitosis produce

Answer 1

Produces TWO daughter cells with the SAME number of chromosomes as the parent cell and eachother

Question 2

What does Meiosis produce

Answer 2

Produces FOUR daughter cells with HALF the number of chromosomes as the parent cell

Question 3

Where does mitosis occur

Answer 3

All cells but sex cells, and red blood cells

Question 4

Why is meiosis necessary

Answer 4

In sexual reproduction, two gametes fuse together to form new offspring.

To maintain a constant number of chromosomes in the adult of species, it is important that the number of chromosomes is halved at some point

Question 5

When does halving of the chromosome number take place

Answer 5

During Meosis

Question 6

Where does meiosis occur

Answer 6

Testes and Ovum - Sperm and egg cell

Some plants this occurs during spore production

Question 7

What do diploid cells contain

Answer 7

Two complete sets of chromosomes, one from each parent

Question 8

What stages are involved in meiosis

Answer 8

Meiosis 1:

Homologous chromosomes pair up and their chromatids wrap around one another

Equivalent portions of each chromatid may cross over

Meoisis 2:

The chromatids move apart, 4 cells are formed

Question 9

What is the process of Meiosis 1

Answer 9

1. Homologous chromosomes pair up and their chromatids wrap around eachother - Equivalent portions of each chromatid may be exchanged during this process
2. By the end of this process, the homologous pairs have separated with one chromosome from each pair entering one of the two daughter cells

Question 10

Products of Meiosis 1

Answer 10

2 daughter cells

Question 11

What is the process of meiosis 2

Answer 11

1. Chromatids move apart

2. Four daughter cells are formed - each containing 23 chromosomes

Question 12

How does meiosis led to genetic variation occuring (3 ways)

Answer 12

1. Independent segregation of homologous chromosomes
2. Crossing over
3. Variety of new genetic combinations

Question 13

What is a gene

Answer 13

A section of DNA that codes for a polypeptide

Question 14

What is a locus

Answer 14

The position of a gene on a chromosome or DNA molecule

Question 15

Allele

Answer 15

Variation of a gene

Question 16

Homologous chromosome

Answer 16

A pair of chromosomes, one maternal, one paternal, that have the same gene loci

Question 17

Variation by independent segregation of homologous chromosomes

Answer 17

1. During meiosis 1, each chromosome lines up alongside its homologous partner
2. When they line themselves up, it is done at random. One of each pair will pass into each of the daughter cells. Which one of the pair goes into the daughter cell depends on how many pairs are lined up in a parent cell
3. The lining up of pairs is random, therefore the combination of chromosomes of maternal and paternal origin that go into the daughter cell is a matter of chance

Question 18

Variety of new Genetic combinations

Answer 18

Each member of a homoloogus pair has exactly the same genes. However, the alleles of these genes differ

The independent assortment of these chromosomes therefore produces new combinations

Question 19

Genetic combination by crossing over

Answer 19

During meiosis 1, each chromosome lines up.

1. The chromatids of each pair become twisted around each other
2. During this twisting process, tensions are created and portions of the chromatids break off
3. The equivalent portions of homologous chromosomes are exchanged
4. In this way, new combinations are formed

Question 20

How to calculate the number of possible combinations for each daughter cell

Answer 20

2^n, n = Number of homologous pairs

Question 21

How to calculate the possible combinations when two different parents come together

Answer 21

(2^n)^2, n = Number of homologous pairs