3.4.3 Genetic diversity can arise as a result of
mutation or during meiosis
Genetic variation can be introduced in many ways, such as:
1) Meiosis
2) Mutations
3) Random fertilisation of gametes
Meiosis
Meiosis produces 4 haploid daughter cells that are genetically different to each other
(unique). There are 2 nuclear divisions- 4 haploid daughter cells from 1 parent cell.
In the first division (meiosis I) - homologous chromosomes are separated - these are the
pair of chromosomes you inherit - one from each parent - they are the same type of
chromosome - same gene but may be different versions of the gene - same gene loci .
In the second division (meiosis II) - the sister chromatids of each chromosomes are
separated
First division - homologous chromosomes separate
Second division - sister chromatids separate
You do not need to know about PMAT here, only about how genetic variation is introduced!
(phew…)
There are 2 main mechanisms through which this occurs (both occur in meiosis I):
1) Independent segregation of homologous chromosomes
In meiosis I, homologous pairs of chromosomes line up opposite to each other at the
equator of the cell. Which side of the equator the paternal and maternal
chromosomes line up is random however homologous pairs are next to each other.
These pairs are separated so that one of each homologous pair ends up in the the
daughter cell - each daughter cell is genetically unique
Different combinations of maternal paternal chromosomes so a mix of different
alleles for different genes
2^n → where n is the number of homologous pairs. This is used to
calculate the number of possible combinations of chromosomes in the
daughter cell produced
Square this number to find the amount of combinations when male and female
gametes combine
2) Crossing over between homologous chromosomes
This introduced further genetic variation.
