Meiosis and Genetic Variation

Question 1

What are gametes?

Answer 1

Sperm cells in males and egg cells in females

Question 2

What do gametes join at fertilisation to join?

Answer 2

Zygotes

Question 3

Normal body cells have what number of chromosomes?

Answer 3

Diploid number (2n) of chromosomes - each cell contains two of each chromosomes

Question 4

Gametes have a what number of chromosomes?

Answer 4

Haploid (n) number of chromosomes

Question 5

Fertilisation is what?

Answer 5

Random

Question 6

hat does random fertilisation produce?

Answer 6

Zygotes with different combinations of chromosomes to both parents

Question 7

Explain meiosis

Answer 7

1. Before meiosis starts, DNA unravels and replicates so there are two copies of each chromosome, called chromatids
2. DNA condenses to form double-armed chromosomes, each made from two sister chromatids, joined in the middle by a centromere
3. Meiosis I - the chromosomes arrange themselves into homologous pairs
4. The homologous pairs are them separated, halving the chromosome number
5. Meiosis II - the pairs of sister chromatids that make up each chromosome are separated
6. Four haploid cells that are genetically different from each other are produced

Question 8

Explain crossing over

Answer 8

In meiosis I, homologous pairs of chromosomes pair up. The chromatids twist around each other and bits of chromatid swap over. The chromatids contain the same genes but different combinations of alleles

Question 9

What two things in meiosis lead to genetic variation?

Answer 9

1. Crossing over of chromatids
2. Independent segregation of chromosomes

Question 10

Explain independent segregation of chromosomes

Answer 10

1. Each homologous pair of chromosomes if made up of one maternal and one paternal chromosome
2. When the homologous pairs are separated in meiosis I its random which chromosome from each pair ends up in each daughter cell
3. The four daughter cells produced by meiosis have different combinations of maternal and paternal chromosomes
4. This ‘shuffling’ of chromosomes leads to genetic variation

Question 11

What is chromosome mutation?

Answer 11

When there are errors during meiosis and the cells produce contain variations in the numbers of whole chromosomes or parts of chromosomes