Navigation Links
Allele frequency

Allele frequency is a term of population genetics that is used in characterizing the genetic diversity of a species population, or equivalently the richness of its gene pool. Allele frequency is defined as follows:

Given a) a particular chromosome locus, b) a gene occupying that locus, c) a population of individuals carrying n loci in each of their somatic cells (e.g. two loci in the cells of diploid species, which contain two sets of chromosomes) and finally d) a variant or allele of the gene, then the allele frequency of that allele is the fraction or percentage of loci that the allele occupies within the population.

To take an example, if the frequency of an allele is 20% in a given population, then among population members, one in five chromosomes will carry that allele. Four out of five will be occupied by other variants the gene, of which there may be one or many.

Note that for diploid genes, however, the proportion of individuals that carry this allele may be up to two in five. If the allele distributes randomly, then the binomial theorem will apply: 32% of the population will be heterozygous for the allele (i.e. carry one copy of that allele and one copy of another in each somatic cell) and 4% will be homozygous (carrying two copies of the allele). So all together 36% of diploid individuals would be expected to carry an allele that has a frequency of 20%. However, alleles distribute randomly only in the absence of selection and under other assumptions. When these conditions apply, a population is said to be in Hardy-Weinberg equilibrium.

The frequencies of all the alleles of a given gene often are graphed together as an allele frequency distribution histogram. Population genetics studies the different "forces" that might lead to changes in the distribution and frequencies of alleles -- in other words, to evolution. Besides selection, these forces include genetic drift, mutation and migration.

Compare genotype frequency.


If there are ten individuals in a population and at a given locus there are two possible alleles, A and a, then if the genotypes of the individuals are:

AA, Aa, AA, aa, Aa, AA, AA, Aa, Aa, and AA

then the allele frequencies of allele A and allele a are:

pA = (2+1+2+0+1+2+2+1+1+2)/20 = 0.7
pa = (0+1+0+2+1+0+0+1+1+0)/20 = 0.3


(Date:4/23/2014)... Toronto Scarborough research shows that male black widow spiders ... a rare example of mate preference by male spiders. ... Emily MacLeod and Maydianne Andrade, a professor in UTSC,s ... studies and the wild that males overwhelmingly chose to ... black widows can tell whether a potential mate is ...
(Date:4/23/2014)... Scientists have conclusive evidence that the source of a ... Ocean and called the "bio-duck," is the Antarctic minke ... by submarine personnel in the 1960s who thought it ... recorded at various locations in the Southern Ocean, but ... In February 2013, an international team of researchers deployed ...
(Date:4/23/2014)... accurate group decision increases with the abundance of brains ... a variety of factors as often happens in ... smaller groups actually tend to make more accurate decisions ... certain pieces of information. , The findings present a ... or the "wisdom of crowds," wherein individual observations ...
Breaking Biology News(10 mins):Picky male black widow spiders prefer well-fed virgins 2Scientists identify source of mysterious sound in the Southern Ocean 2Scientists identify source of mysterious sound in the Southern Ocean 3Too many chefs: Smaller groups exhibit more accurate decision-making 2Too many chefs: Smaller groups exhibit more accurate decision-making 3
... ARBOR, Mich. Researchers from the University of Michigan ... overexpressed in 90 percent of pancreatic cancers, the most ... Ataxia Telangiectasia Group D Complementing gene, called ATDC, is ... than in cells from a normal pancreas. What,s more, ...
... Germany March 2, 2009 >> Genomatix Software, a ... Next Generation Sequencing (NGS) data, announced today that Boehringer ... Mining Station and a Genomatix Genome Analyzer at its ... the only complete and integrated analysis solution for NGS ...
... of Illinois plant geneticist Stephen Moose has developed a corn ... that would make good silage, Moose said, due to a ... make it a good energy crop. The gene known ... giving corn seedlings a waxy coating that acts like a ...
Cached Biology News:U-M researchers ID gene involved in pancreatic cancer 2Boehringer Ingelheim uses Genomatix' Next Generation Sequencing data analysis systems 2Doubling a gene in corn results in giant biomass 2
Other biology definitionOther Tags