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The McDonald–Kreitman test [1] is a statistical test often used by evolutionary and population biologists to detect and measure the amount of adaptive evolution within a species by determining whether adaptive evolution has occurred, and the proportion of substitutions that resulted from positive selection (also known as directional selection).
In genetics, a selective sweep is the process through which a new beneficial mutation that increases its frequency and becomes fixed (i.e., reaches a frequency of 1) in the population leads to the reduction or elimination of genetic variation among nucleotide sequences that are near the mutation.
Example for a trait under positive selection. The Price equation shows that a change in the average amount of a trait in a population from one generation to the next is determined by the covariance between the amounts of the trait for subpopulation and the fitnesses of the subpopulations, together with the expected change in the amount of the trait value due to fitness, namely ():
The way to accurately estimate the average strength of positive selection acting on the human genome is by inferring the distribution of fitness effects (DFE) of new advantageous mutations in the human genome, but this DFE is difficult to infer because new advantageous mutations are very rare (Boyko et al. 2008).
A ratio greater than 1 implies positive or Darwinian selection (driving change); less than 1 implies purifying or stabilizing selection (acting against change); and a ratio of exactly 1 indicates neutral (i.e. no) selection. However, a combination of positive and purifying selection at different points within the gene or at different times ...
In biology, evolution is change in the heritable characteristics of biological organisms over generations due to natural selection, mutation, gene flow, and genetic drift. Also known as descent with modification .
Frequency-dependent selection is an evolutionary process by which the fitness of a phenotype or genotype depends on the phenotype or genotype composition of a given population. In positive frequency-dependent selection, the fitness of a phenotype or genotype increases as it becomes more common.
Another example of directional selection is the beak size in a specific population of finches. Darwin first observed this in the publication of his book, On the Origin of Species , and he details how the size of the finches beak differs based on environmental factors.