The causes of genetic variations
- Gene reshuffling
- Independent assortment of genes at meiosis I allow gene reshuffling in in two ways
– orientation on the equator in metaphase I
During metaphase I of the first meiotic division homologous chromosomes came together in pairs and subsequently segregate into a daughter cells independently of each other. The result of this independent assortment is the production of the wide variety of different gametes depending on which particular chromosome end up with one another in each cell.
– Crossing over
In prophase of the first meiotic division, homologous chromosomes came together and make intimate contact with each other. Chromatid of homologous chromosome may break and rejoin at any place called chiasmata.
- Fertilization
Union of gametes at fertilization results in alleles present in one gamete being united with alleles in another. If a population consist of large number of out breeding individual, the amount of variation that may result from this is again virtually infinite.
Despite the tremendous amount of variation these three processes may generate, they play only a limited role in evolution. The reason is that although they may establish a new combination of alleles in one generation, they do not generate long lasting variation of a novel kind.
- Mutation
This is a change in the amount or structure of DNA of an organism. This produces a change in the genotype which may be inherited by cells derived by mitosis or meiosis. Individuals showing the new characteristics are referred to as mutants. Mutants arise spontaneously and in no sense ‘directed’ by the environment, although the environment greatly influence the mutation rate.
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Dr. Bbosa Science
