4.8 Meiosis

Question 1

What is sexual reproduction?

Answer 1

Sexual production is when genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent

Question 2

In sexual reproduction, what do the father and other produce?

Answer 2

Gametes

Question 3

What are gametes in animals?

Answer 3

In animals these are sperm and egg cells

Question 4

Gametes only contain ____ the number of chromosomes of normal cells

Answer 4

Half

Question 5

How does fertilisation occur and end with an embryo? (Describe all steps - 2)

Answer 5

• At fertilisation, a male gamete fuses with a female gamete to produce a fertilised egg, known as a zygote. Chromosomes from the mother pair up with chromosomes with the father, so the zygote ends up with the full set of chromosomes
• The zygote then undergoes cell division (by mitosis) and develops into an embryo

Question 6

Why does the embryo inherit characteristics from both parents?

Answer 6

The embryo inherits characteristics from both parents as its received a mixture of chromosomes (and therefore genes) from its mum and dad

Question 7

What does meiosis produce?

Answer 7

It produces genetically different cells with half the chromosomes of the original cell.

Question 8

In humans, where does meiosis happen?

Answer 8

Meiosis only happens in the reproductive organs (ovaries and testes)

Question 9

What are the chromosomes from the mother called?

Answer 9

Maternal chromosomes

Question 10

What are the chromosomes from the father called?

Answer 10

Paternal chromosomes

Question 11

Before meiosis can begin, what does the cell go through?

Answer 11

Interphase

Question 12

During interphase, what happens? (Division 1)

Answer 12

During this period it duplicates its DNA (so there’s enough for each new cell). One arm of each X-shaped Chromosome is an exact copy of the other arm.

Question 13

What step takes place after the interphase? (Division 1)

Answer 13

In the first division in meiosis, the chromosomes line up in pairs in the centre of the cell. One chromosome in each pair came from the organism’s mother and one came from its father

Question 14

What step takes place after the chromosomes line up in pairs down the centre of the cell? (Division 1)

Answer 14

The pairs are then pulled apart, so each new cell ends up with one chromosome from each pair. Some of the father’s chromosomes and some of the mother’s chromosomes go into each new cell

Question 15

Why is it important that in the third step of division 1 the genes are mixed up?

Answer 15

It creates genetic variation in the offspring (i.e. each offspring will have a different mixture of alleles)

Question 16

What happens in division 2? (2)

Answer 16

• In the second division, the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart
• You get four gametes - each only has a single set of chromosomes (23). The gametes are all genetically different

Question 17

What is another name for a gamete cell?

Answer 17

Haploid cell

Question 18

Why are gametes also called haploid cells?

Answer 18

They contain half the genetic material of a normal cell

Question 19

What is another name for a normal cell made by two gametes combining?

Answer 19

Diploid cell

Question 20

Why are normal cells formed by two gametes combining also called diploid cells?

Answer 20

They contain two sets of genetic information - one from each parent

Question 21

How many chromosomes does a human gamete have?

Answer 21

23

Question 22

As a result of meiosis, how many cells are produced?

Answer 22

4