Mutational Change in Evolution

Abstract

Evolution is the process of change in the genetic make‐up of populations. Two evolutionary forces are known to cause changes in gene frequencies with time: selection and random genetic drift.

Keywords: mutation; selection; drift; population; substitution

Figure 1.

Changes in the frequency of an advantageous allele A2 under (a) codominant selection, (b) dominant selection where A2 is dominant over A1 and (c) dominant selection where A1 is dominant over A2. In all cases, the frequency of A2 at time 0 is q=0.04, and the selective advantage is s=0.01.

Figure 2.

(a) Changes in the frequency of an allele subject to overdominant selection. Initial frequencies from top to bottom curves: 0.99, 0.75, 0.50, 0.25 and 0.01; s=0.04 and t=0.02. Since the s and t values are exceptionally large, the change in allele frequency is rapid. Note that there is a stable equilibrium at q=0.667. (b) Changes in the frequency of an allele subject to underdominant selection. Initial frequencies from top to bottom curves: 0.75, 0.668, 0.667, 0.666, 0.50 and 0.20; s=−0.02 and t=−0.01. Again, because of the large values of s and t, the change in allele frequency is rapid. Note that there is an equilibrium at q=0.667. This equilibrium, however, is unstable since even the slightest deviation from it will cause one of the alleles to be eliminated from the population.

Figure 3.

Random sampling of gametes. Allele frequencies in the gamete pools (large boxes) in each generation are assumed to reflect exactly the allele frequencies in the adults of the parental generation (small boxes). Since the population size is finite, allele frequencies fluctuate up and down. (Bodmer WF and Cavalli‐Sforza LL (1976) Genetics, Evolution, and Man. San Francisco: Freeman.)

Figure 4.

Changes in frequencies of alleles subject to random genetic drift in populations of different sizes. The smallest population reached fixation after 42 generations. The other two populations were still polymorphic after 150 generations but will ultimately reach fixation (allele frequency=0 or 100%) if the experiment is continued long enough. (Bodmer WF and Cavalli‐Sforza LL (1976) Genetics, Evolution, and Man. San Francisco: Freeman.)

Figure 5.

Two possible outcomes of random genetic drift in populations of size 25 and p0=0.5.

Figure 6.

Schematic representation of the dynamics of gene substitution for (a) advantageous and (b) neutral mutations. Advantageous mutations are either quickly lost from the population or quickly fixed, so that their contribution to genetic polymorphism is small. The frequency of neutral alleles, however, changes very slowly in comparison, so that a large amount of transient polymorphism is generated, is the conditional fixation time, and 1/K is the mean time between two consecutive fixation events. (Nei M (1987) Molecular Evolutionary Genetics. New York: Columbia University Press.)

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Further Reading

Gillespie JH (1991) The Causes of Molecular Evolution. New York, NY: Oxford University Press.

Gillespie JH (1998) Population Genetics: A Concise Guide. Baltimore, MD: Johns Hopkins University Press.

Graur D and Li W‐H (2000) Fundamentals of Molecular Evolution, 2nd edn. Sunderland, MA: Sinauer Associates.

Hartl DL and Clark AG (2007) Principles of Population Genetics, 4th edn. Sunderland, MA: Sinauer Associates.

Hedrick PW (2005) Genetics of Populations, 3rd edn. Sudbury, MA: Jones and Bartlett Publishers.

Hey J (1999) The neutralist, the fly and the selectionist. Trends in Ecological Evolution 14: 35–38.

Kimura M (1962) On the probability of fixation of mutant genes in populations. Genetics 47: 713–719.

Kimura M (1968a) Evolutionary rate at the molecular level. Nature 217: 624–626.

Kimura M (1968b) Genetic variability maintained in a finite population due to mutational production of neutral and nearly neutral isoalleles. Genetic Research 11: 247–269.

Kimura M (1983) The Neutral Theory of Molecular Evolution. Cambridge: Cambridge University Press.

Kimura M and Ohta T (1969) The average number of generations until fixation of a mutant gene in a finite population. Genetics 61: 763–771.

King JL and Jukes TH (1969) Non‐Darwinian evolution. Science 164: 788–798.

Schwartz MK, Tallmon DA and Luikart G (1998) Review of DNA‐based census and effective population size estimators. Animal Conservation 1: 293–299.

Wright S (1931) Evolution in Mendelian populations. Genetics 16: 97–159.

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How to Cite close
Graur, Dan(Apr 2008) Mutational Change in Evolution. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0005092.pub2]