Genetic variability

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Genetic variability is a measure of the tendency of individuals in a population to vary from one another. Variability is different from genetic variation, which is the actual amount of variation seen in a particular population.[1] The variability of a trait describes how much that trait tends to vary in response to changes in the genetics of a population.[1] Genetic variability in a population is very important, because without variability, it becomes difficult for a population to adapt to environmental changes, creating a static population. Variability is an important factor in evolution since it provides the potential for genetic variation, the raw material for natural selection.

[edit] Causes of Variability

There are many sources of genetic variability in a population:

  • Genetic recombination is one source of variability; during meiosis in sexual creatures two homologous chromosomes from the male and the female cross over one another and exchange gene sequences. The chromosomes then split apart and are ready to form an offspring. The cross-over is random and is governed by its own set of genes that code for where crossovers can occur (in cis) and for the mechanism behind the exchange of DNA chunks (in trans). Being controlled by genes means that recombination is also variable in frequency, location, thus it can be selected to increase fitness by nature, because the more recombination the more variability and the more variability the easier it is for the population to handle changes.[2]
  • Immigration, emigration, and translocation – each of these is the movement of an individual into or out of a population. When an individual comes from a previously genetically isolated population into a new one it will increase the genetic variability of the next generation if it reproduces.[3]
  • Polyploidy – having more than two homologous chromosomes allows for even more recombination during meiosis allowing for even more genetic variability in one's offspring.
  • Diffuse centromeres – in asexual organisms where the offspring is an exact genetic copy of the parent, there are limited sources of genetic variability. One thing that increased variability, however, is having diffused instead of localized centromeres. Being diffused allows the chromatids to split apart in many different ways allowing for chromosome fragmentation and polyploidy creating more variability.[4]
  • Genetic mutations – mutations are accidental mistakes made in transcription, translation, and all the other processes that DNA and RNA are put through before the creation of a protein. They can be positive, negative, or neutral in regards to fitness, and because they are random they contribute to the genetic variability within a population.[5] This variability can be easily propagated throughout a population by natural selection if the mutation increases the affected individual's fitness and its effects will be minimized/hidden if the mutation is deleterious. However, the smaller a population and its genetic variability are, the more likely the recessive/hidden deleterious mutations will show up causing genetic drift.[5]



[edit] References

  1. ^ a b (1995) Variation and Variability. Yale University. Retrieved on 2007-05-24. 
  2. ^ Burt, Austin (2000). "Perspective: Sex, Recombination, and the Efficacy of Selection—Was Weismann Right?". Evolution: International Journal of Organic Evolution (54.2): 337–351. 
  3. ^ Ehrich, Dorothy and Per Erik Jorde (2005). "High Genetic Variability Despite High-Amplitude Population Cycles in Lemmings". Journal of Mammalogy (86.2): 380–385. doi:10.1644/BER-126.1. 
  4. ^ Linhart, Yan and Janet Gehring (2003). "Genetic Variability and its Ecological Implications in the Clonal Plant Carex scopulurum Holm. In Colorado Tundra". Arctic, Antarctic and Alpine Research (35.4): 429–433. doi:10.1657/1523-0430(2003)035[0429:GVAIEI]2.0.CO;2. 
  5. ^ a b Wills, Christopher (1980). Genetic Variability. NewYork: Oxford University Press.