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Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone. Balancing selection is rare compared to purifying selection. [1]
The incidental purging of non-deleterious alleles due to such spatial proximity to deleterious alleles is called background selection. [4] This effect increases with lower mutation rate but decreases with higher recombination rate. [5] Purifying selection can be split into purging by non-random mating (assortative mating) and purging by genetic ...
Downstream processing refers to purification of chemicals, pharmaceuticals and food ingredients produced by fermentation or synthesized by plant and animal tissues, for example antibiotics, citric acid, vitamin E, and insulin.
In negative frequency-dependent selection, the fitness of a phenotype or genotype decreases as it becomes more common. This is an example of balancing selection. More generally, frequency-dependent selection includes when biological interactions make an individual's fitness depend on the frequencies of other phenotypes or genotypes in the ...
Stabilizing selection (not to be confused with negative or purifying selection [1] [2]) is a type of natural selection in which the population mean stabilizes on a particular non-extreme trait value. This is thought to be the most common mechanism of action for natural selection because most traits do not appear to change drastically over time. [3]
Purifying or negative selection acts to remove genetic variation from the population (and is opposed by de novo mutation, which introduces new variation. [76] [77] In contrast, balancing selection acts to maintain genetic variation in a population, even in the absence of de novo mutation, by negative frequency-dependent selection.
For example, if K a /K s = 1, it could be due to relaxed selection, or to a chimera of positive and purifying selection at the locus. A solution to this limitation would be to apply K a /K s analysis across many species at individual codons. The K a /K s method requires a rather strong signal in
For many decades, Lyster's method remained the standard for U.S. ground forces in the field and in camps, implemented in the form of the familiar Lyster Bag (also spelled Lister Bag). The bag was made of canvas and could hold 36 gallons of water. It was porous and held up by ropes, purifying water with the help of calcium hypochlorite solution.