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:9/23/2014)... CHAMPAIGN, Ill. Scientists have scoured cow rumens and ... plant cell walls for the production of next-generation biofuels, ... reside in the human lower intestine, researchers report. , ... of the National Academy of Sciences , is the ... that microbes in the human gut can digest fiber, ...
(Date:9/23/2014)... Arguments about whose turn it is to do the washing ... over noise as many students returning to university for ... way, sharing a house can be a tricky business. , ... has revealed that new technology to allow people to monitor ... ratchet up the tension. , The study by a team ...
(Date:9/23/2014)... majority of drugs used to treat asthma today are the ... are urgently needed to treat this chronic respiratory disease, which ... to wheeze, cough, and find it difficult at best to ... is tough: asthma is a patient-specific disease, so what works ... animal models traditionally used to test new drug candidates often ...
Breaking Biology News(10 mins):Search for better biofuels microbes leads to the human gut 2Search for better biofuels microbes leads to the human gut 3Smart meters could cause conflict for housemates, study shows 2Smart meters could cause conflict for housemates, study shows 3Airway muscle-on-a-chip mimics asthma 2Airway muscle-on-a-chip mimics asthma 3
... the wind, but a new study in the October 14th ... confirms that they are anything but drifters. A previous ... evidence that Silver Y moths rely on a sophisticated internal ... destination within a matter of days. Now, the research team ...
... mouse heart has an astounding capacity to regenerate, ... The research, published by Cell Press in the ... Cell , describes the previously unrecognized potential of ... compensatory proliferation of healthy cells. Disorders of ...
... why people who eat more fruit and vegetables may gain ... that a fragment released from pectin, found in all fruits ... 3 (Gal3), a protein that plays a role in all ... effects of foods are based on population studies," says Professor ...
Cached Biology News:Migratory moths may hitch their rides, but they're anything but drifters 2Embryonic heart exhibits impressive regenerative capacity 2Pectin power 2
Other biology definitionOther Tags