Meiosis and Genetic Variation

Question 1

Gametes are haploids rather than diploids. What does this mean?

Answer 1

They only have one copy of each chromosome

Question 2

Why is it important that gametes have a haploid number of chromosomes?

Answer 2

During fertilisation the sperm and egg join to make a diploid cell (zygote) Correct number of chromosomes - 1 from each parent

Question 3

How does fertilisation increase genetic diversity?

Answer 3

Fertilisation is random. Produces zygote with combination of chromosomes from each parent

Question 4

How are gametes formed?

Answer 4

Meiosis

Question 5

Where does meiosis take place?

Answer 5

In the reproductive organs

Question 6

How many pairs of chromosomes do humans have?

Answer 6

23 pairs (46 chromosomes in total)

Question 7

What are homologous pairs?

Answer 7

Two chromosomes which make up a pair
1 inherited from each parent
Chromosomes are same size and same genes, but different alleles

Question 8

How does the crossing over of chromatids during meiosis 1 lead to variation?

Answer 8

The homologous pairs come together and twist around each other
Some parts of chromatids swap over
Same genes but different combination of alleles

Question 9

Apart from the crossing over of chromatids, how else does meiosis produce genetically different cells?

Answer 9

Independent segregation of chromosomes

Question 10

What is the independent segregation of chromosomes?

Answer 10

The homologous pairs split during meiosis 1
It is random which pair ends up in which daughter cell
The shuffling of these chromosomes leads to variation in potential offspring

Question 11

Give three ways in which meiosis and mitosis differ

Answer 11

Mitosis produces diploid cells, meiosis produces haploid cells
Mitosis produces 2 daughter cells, meiosis produces 4 daughter cells
Mitosis produces genetically identical cells, meiosis produces genetically different cells

Question 12

What happens during meiosis 1?

Answer 12

The homologous pairs are split up. The number of chromosomes is halved

Question 13

What happens during meiosis 2?

Answer 13

The pairs of sister chromatids are separated and the cells divide again

Question 14

How is Down’s syndrome caused?

Answer 14

Non-disjunction of chromosomes

Three copies of chromosome 21

Question 15

What is a chromatid?

Answer 15

One-half of two identical strands of a replicated chromosome