8.4 Meiosis And Genetic Variation

Question 0

In which ways does the division of the nucleus of cells occur?

Answer 0

1. Mitosis: produces two daughter nuclei with the same number of chromosomes as the parent cell.
2. Meiosis: produces four daughter nuclei, each with half the number of chromosomes as the parent cell.

Question 1

What two components make up the division of a cell?

Answer 1

1. The division of the nucleus

2. The division of the cell as a whole

Question 2

Why is halving the number of chromosomes necessary in meiosis?

Answer 2

In order to maintain a constant number of chromosomes in the adult species.

Question 3

How many chromosomes does a human diploid cell have?

Answer 3

46 (23 homologous pairs)

Question 4

How many chromosomes does a human haploid cell have?

Answer 4

23 chromosomes

Question 5

How is the diploid number restored at fertilisation?

Answer 5

Two haploid gametes fuse.

Question 6

Describe the two nuclear divisions of meiosis.

Answer 6

1. In meiosis 1, the homologous chromosomes pair up and their chromatids wrap around each other.

Crossing over occurs where equivalent proportions of these chromatids are exchanged.

The homologous pairs separate, with one chromosome from each pair going into one of the two daughter cells

2. In meiosis 2, the chromatids move apart.

Question 7

How does meiosis produce genetic variation among offspring to allow an organism to adapt and survive in a changing world?

Answer 7

Independent segregation of homologous chromosomes

Recombination of homologous chromosomes by crossing over

Question 8

Describe independent segregation.

Answer 8

In meiosis 1 each chromosome lines up alongside its homologous partner - arranged randomly.
One of each pair will pass to each daughter cell, this depends on how the pairs are lined up in the parent cell.

Since the pairs are lined up at random, the combination of chromosomes that goes into the daughter cell at meiosis 1 is also random. This is independent segregation.

Question 9

New….

Answer 9

Genetic combinations are produced as a result of the different alleles on the homologous chromosomes. E.g brown eyes and blood type A

Question 10

What is the saying for meiosis?

Answer 10

Homologous pair
Double
Cuddle
Split
Split

HDCSS
Hi dick cocks suck sick

Question 11

How does crossing over occur?

Answer 11

The chromatids of each pair become twisted around each other
Tensions are created and portions of the chromatids break off
The homologous pairs rejoin
In this way new genetic combinations are produced

Question 12

During crossing over, broken-off portions of chromatid recombine with another chromatid. What is this process called?

Answer 12

Recombination

Question 13

Crossing over increases…

Answer 13

Genetic variety

Question 14

In meiosis, If crossing over occurs there is four different types of cell produced. If it does not occur there are…

Answer 14

Only two different types of cell produced.