GENETIC VARIABILITY AND MUTATION Genetic variability or genetic variation involves the differences in DNA among individuals. If there was no genetic variation, the organisms of the same species would always look alike. Genetic variation can be seen phenotypically, found through biochemical differences, or seen in the DNA sequencing of the organisms. Geographic variation can be seen in populations that are of the same species but do not look alike. This is because of genetic drift. Most genetic variation is caused by random mutations. There are a number of ways to maintain genetic variation in a population. Because of heterozygosity, alleles that may be harmful and that are recessive can be somewhat hidden. Natural selection also favors genetic variation. Genetic variation can be helpful because it promotes biodiversity. Other things that can cause genetic variability include the following: •
Recombination among homologous chromosomes.
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Movement into or out of a population.
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Polyploidy, which is having more than two of the same chromosomes.
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Genetic mutations that have a positive effect on fitness.
In actuality, mutations happen all the time. About 60,000 mutations occur every day in human cells in each cell but the majority of these are repaired with DNA repair mechanisms. Things that decrease genetic variability include the following: •
Fragmentation of the habitat of an organism.
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The founder effect, in which a population is founded by just a few individuals.
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Climate change, which decreases the size of populations and lowers variability.
Evolvability is when a system or population is able to undergo adaptive evolution. This allows for evolution through natural selection. If beneficial mutations do not happen often enough, adaptation can t occur. Sexual reproduction causes more evolvability than asexual reproduction. Selection is better and is enhanced because of things like mating rituals that increase sexual selection, having a large population size, short generation time, and recombination.
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