Meiosis and Genetic Variation

Question 1

define gametes

Answer 1

sex cells found in female and male organisms which join together at fertilisation to form a zygote, which then develops into a new organism

Question 2

how many chromosomes do normal body cells have?

Answer 2

diploid number (2n)

Question 3

how many chromosomes do gamete cells have?

Answer 3

haploid number (n)

Question 4

how are gametes formed?

Answer 4

formed by meiosis, a type of cell division which occurs in the reproduction organs

Question 5

describe the process of meiosis

Answer 5

1. Before meiosis, DNA unravels and replicates so there’s two chromatids
2. DNA condenses to form double armed chromosomes, joined at the centre by a centromere, sister chromatids
3. In Meiosis I, the chromosomes arrange themselves into homologous pairs, lining up at the equator
4. These homologous pairs are then separated halving the chromosome number
5. In Meiosis II, the pairs of sister chromatids are separated meaning the centromere is divided
6. Four haploid cells, that are genetically different from each other are produced

Question 6

define sister chromatids

Answer 6

two identical copies of the same chromosome, attached together via a centromere

Question 7

define homologous pairs

Answer 7

one paternal and maternal chromatid, with the same genes, just a different combination of alleles, attached via the centromere

Question 8

what are the two main ways genetic variation can occur during mitosis?

Answer 8

• crossing over
• independent segregation of chromosomes

Question 9

what is crossing over?

Answer 9

the process where during the formation of homologous chromosomes, the chromatids twist, meaning bits of chromatids swap over, its still the same gene, just a different combination of alleles

Question 10

what is independent segregation of chromosomes?

Answer 10

the idea that during Meiosis I, the order in which homologous pairs line up at the equator is random

Question 11

what are chromosome mutations?

Answer 11

mutations that are caused by errors within cell division that can lead to variation

Question 12

what can chromosome mutations lead to?

Answer 12

inherited conditions, due to errors present in the gametes

Question 13

give an example of a hereditary disease

Answer 13

downs syndrome, caused by an extra copy of a chromosome