How is variation achieved in meiosis?
1. Crossing over / recombination
Crossing over, or recombination, is the exchange of chromosome segments between nonsister chromatids in meiosis. Crossing over creates new combinations of genes in the gametes that are not found in either parent, contributing to genetic diversity.
2. Independent assortment a
During metaphase I, the bivalents move to the metaphase plate. The homologous pairs orient themselves randomly at the equator. In each cell that undergoes meiosis, the arrangement of the chromosomes is different. The number of variations is dependent on the number of chromosomes making up a set with the possible number of alignments equalling 2n, where n is the number of chromosomes per set.
2. Independent assortment b
During metaphase II, there is further random distribution and subsequent separation of the sister chromatids.
3. Random fertilisation
Genetic variation is also introduced by random fertilisation of the gametes produced by meiosis. Any of the genetically unique sperm generated by a male may fertilise the genetically unique egg produced by a female.
