9.2 Meiosis And Genetic Variation

Question 1

What are gametes?

Answer 1

• sperm cells in males
• egg cells in females
• join together at fertilisation to form a zygote = new organism

Question 2

How many chromosomes do body cells contain?

Answer 2

• 46 chromosomes
• diploid number (2n)
• one maternal and one paternal

Question 3

How many chromosomes to gametes contain?

Answer 3

• 23 chromosomes
• haploid number (n)
• only one copy

Question 4

What happens at fertilisation?

Answer 4

• haploid sperm fuses with haploid egg = diploid chromosome number
• half from sperm and half from egg

Question 5

What happens at sexual reproduction?

Answer 5

• any sperm can fertilisation any egg = random
• random fertilisation produces zygotes with different combinations of chromosomes
• mixing genetic material increases genetic diversity within species

Question 6

What is meiosis?

Answer 6

• type of cell division that produces four daughter cells
• happens in reproductive organs

Question 7

Describe the process of meiosis

Answer 7

1. DNA unravels and replicates creating two copies = chromatids
2. DNA condenses to form a chromosome with two chromatids that are joined by a centromere
3. Meiosis I = homologous chromosomes arrange themselves in pairs
4. Homologous pairs are separated = halving chromosome number
5. Meiosis II = pair of sister chromatids are separated as centromere divides
6. Four haploid cells (gametes) are produced and genetically different

Question 8

What is independent segregation?

Answer 8

• pairs of homologous chromosomes line up on the spindle in random orientation
• increases genetic variation as results in 4 gametes that carry different combinations of chromosomes

Question 9

What is crossing over?

Answer 9

• chromatids break
• detached part swap over and recombine with different chromosome
• forming a chiasmata
• increases genetic variation as produces 4 sister chromatids that each carry a different combination of alleles