Cell cycle T3

Question 1

What is the purpose of meiosis?

Answer 1

• Process by which a diploid nucleus (2n) divides to produce 4 haploid nuclei which are not genetically identical to each other, or parent.
• Produces gametes.
• Results in genetic variation.

Question 2

What are the stages of meiosis?

Answer 2

• Follows G2 stage of interphase.
• DNA rep has already occurred.
• Meiosis 1 division (homologous pairs sep.), followed be meiosis 2 division (sister chromatids sep.).

Question 3

Discuss the ways in which genetic variation is produced, including the role of nuclear division.
(9)

Answer 3

• Independent assortment of homologous chromosomes in meiosis 1/metaphase 1.
• Independent assortment of sister chromatids in meiosis 2/metaphase 2.
• So homologous chromosomes have different alleles.
• Produces a large number of allele combinations.
• Crossing over/formation of chiasmata.
• In prophase 1/meiosis 1. So chromatids will have new combination’s of alleles.
• Amount of variation depends on distance from cross over points.
• Mutation, changes base sequence of DNA.
• DNA checks during duplication did not recognise damage.
• Change in primary structure/amino acid sequence.
• One more/less chromosomes present.
• Random fertilisation/fusion of gametes.
• Gametes are not genetically identical.
• Produces large number of allele combinations.