NationMaster - Encyclopedia: Stabilizing selection

Stabilizing selection, also referred to as purifying selection, is a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value. Put another way, extreme values of the character are selected against. This is probably the most common mechanism of action for natural selection. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... For other uses, see Natural selection (disambiguation). ... Genetic diversity is a characteristic of ecosystems and gene pools that describes an attribute which is commonly held to be advantageous for survival -- that there are many different versions of otherwise similar organisms. ... In biology, a trait or character is a genetically inherited feature of an organism. ...

A classic example of this is human birth weight. Babies of low weight lose heat more quickly and get ill from infectious disease more easily, whereas babies of large body weight are more difficult to deliver through the pelvis. However, the recent improvements in human nutrition in developed countries has led to rising rates of caesarean sections, since babies are routinely out-growing the female reproductive tract.^[1] World map indicating Human Development Index (as of 2004). ...

Stabilizing selection operates most of the time in most populations. This type of selection acts to prevent divergence of form and function. In this way, the anatomy of some organisms, such as sharks and ferns, has remained largely unchanged for millions of years.

Stabilizing selection can sometimes be detected by measuring the fitness of the range of different phenotypes by various direct measures, but it can also be detected by a variety of tests of molecular sequence data, such as Ka/Ks ratios, changes in allele frequency distributions, and the McDonald Kreitman test.^[2]^[3] Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ... In genetics, the Ka/Ks ratio is the ratio of non-synonymous substitutions (Ka) to synonymous substitutions (Ks), which can be used as an indication of a protein-coding gene. ... Allele frequency is a measure of the relative frequency of an allele on a genetic locus in a population. ...

See also

In population genetics, directional selection (sometimes referred to as positive selection) occurs when natural selection favors a single allele and therefore allele frequency continuously shifts in one direction. ... Disruptive selection is a type of evolution that simultaneously favors individuals at both extremes of the distribution. ...

References

Categories: Selection | Evolution | Evolutionary biology | Ecological processes Molecular evolution is the process of the genetic material in populations of organisms changing over time. ... For other uses, see Natural selection (disambiguation). ... The term background selection refers to the reduction in genetic variation that occurs in the genomic area surrounding a gene that repeatedly mutates to a bad version. ... Sickle-shaped red blood cells Balancing selection refers to forms of natural selection which work to maintain genetic polymorphisms (or multiple alleles) within a population. ... In population genetics, directional selection (sometimes referred to as positive selection) occurs when natural selection favors a single allele and therefore allele frequency continuously shifts in one direction. ... Disruptive selection is a type of evolution that simultaneously favors individuals at both extremes of the distribution. ... It has been suggested that this article or section be merged with Stabilizing selection. ... A selective sweep is the reduction or elimination of variation among the nucleotides in neighbouring DNA of a mutation as the result of recent and strong natural selection. ... A number of different Markov models of DNA sequence evolution have been proposed. ... Models of nucleotide substitution are mathematical equations built to predict the probability (or proportion) of nucleotide change expected in a sequence. ... Allele frequency is a measure of the relative frequency of an allele on a genetic locus in a population. ... In genetics, the Ka/Ks ratio is the ratio of non-synonymous substitutions (Ka) to synonymous substitutions (Ks), which can be used as an indication of a protein-coding gene. ... Tajimas D is a statistical test created by and named after the Japanese researcher Fumio Tajima. ... Gene conversion is a phenomenon which occurs during meiotic division. ... Schematic of a region of a chromosome before and after a duplication event Gene duplication occurs when an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome leads to the duplication of a region of DNA containing a gene [1]. The significance of this process for... Silent mutations or synonymous mutations are DNA mutations that, although they alter a particular codon, they do not alter the final amino acid, and hence do not affect the final protein. ... A synonymous substitution (also called a silent substitution) is the evolutionary substitution of one base for another in an exon of a gene coding for a protein, such that the amino acid sequence produced is not modified. ...