Meiosis and Variation

Question 1

Define meiosis

Answer 1

A type of nuclear division that produces cells that are genetically different. During meiosis, a single cell divides twice but DNA replication only occurs once. 4 cells are produced which are varied and haploid. These are gametes.

Question 2

Describe the process of Meiosis

Answer 2

After interphase, 2 nuclear divisions occur.
➣The 1st meiotic division separates the members of each homologous pair
➣The 2nd meiotic division separates the chromatids of each chromosome

Question 3

Describe Independent Segregation of Homologous Chromosomes

Answer 3

➣Each homologous pair is made from one paternal and one maternal
➣When homologous pairs are separated in Meiosis 1, it’s random which chromosomes from each pair ends up in which daughter cell
➣4 daughter cells have different combinations of those maternal & paternal chromosomes
➣’shuffling’ of chromosomes leads to genetic variation in potential offspring

Question 4

How do you calculate the possible number of varied combinations?

Answer 4

By using 2n, where the number represents the number of homologous pairs. E.G 3 pairs of homologous chromosomes= 2³= 8 possible combinations

Question 5

Describe crossing over

Answer 5

➣Occurs during Prophase of 1st Meiotic division
➣Homologous pairs come together and lie side by side, forming a bivalent. Chromatids intertwine and sometimes break, and so DNA swaps over. This results in the exchange of alleles of the same gene and a new combo known as recombinants.
➣This is known as genetic recombination. The chromosomes then separate. Recombinants are rare as crossing over is rare

Question 6

What processes in meiosis produce cells that are genetically different

Answer 6

➣Independent segregation

➣Crossing over