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.

Example

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:10/14/2014)... A new study published in Cancer Research ... liver and colon cancers—can promote the development of skin ... proliferation and survival of sun-damaged skin cells. , Previously ... seven proteins called sirtuins that help regulate genomic stability ... aging. SIRT6 helps repair DNA damage, which can lead ...
(Date:10/14/2014)... planet,s leading questions is how to produce enough food ... The Food and Agriculture Organization of the United Nations ... next 40 years to feed a growing global population, ... rise in food production. Plants—grains, cereals, fruits, vegetables, ... Current research must tap into our knowledge of ...
(Date:10/14/2014)... 14, 2014 – Scientists from The Scripps Research Institute ... Institutes of Health (NIH) to lead an investigation of ... disease in Africa. The study aims to understand how ... die, while others survive the inflection. , "The ... mechanism of how Lassa fever virus causes disease and ...
Breaking Biology News(10 mins):Two-faced gene: SIRT6 prevents some cancers but promotes sun-induced skin cancer 2Building a bridge from basic botany to applied agriculture 2Building a bridge from basic botany to applied agriculture 3Scripps Research Institute team receives $6.6 million to investigate deadly Lassa virus 2
... October 23, 2008 -- Are green schools acoustically sound? How ... manatees from getting hit by ships? What secrets will comparing ... hidden cars in forests and buried mines underwater? What is ... brain deal with sound? These are a few of ...
... explains the impact,of negative campaigning tactics and the ... conscientiousness are best predictors of,candidate preference and other ... SP Labs - the,research arm of Signal Patterns, ... connect people in meaningful ways -,today released its ...
... on low calorie diets. But now researchers at Washington University ... can extend the life spans of roundworms even when the ... that blocks their sense of smell. Three years ago, ... found that a class of anticonvulsant medications made the roundworm ...
Cached Biology News:156th Acoustical Society of America Meeting, Nov. 10-14, 2008 in Miami 2156th Acoustical Society of America Meeting, Nov. 10-14, 2008 in Miami 3156th Acoustical Society of America Meeting, Nov. 10-14, 2008 in Miami 4156th Acoustical Society of America Meeting, Nov. 10-14, 2008 in Miami 5156th Acoustical Society of America Meeting, Nov. 10-14, 2008 in Miami 6156th Acoustical Society of America Meeting, Nov. 10-14, 2008 in Miami 7New Study Reveals the Emotional Impact and Effectiveness of Negative Campaigning 2New Study Reveals the Emotional Impact and Effectiveness of Negative Campaigning 3New Study Reveals the Emotional Impact and Effectiveness of Negative Campaigning 4Deprived of a sense of smell, worms live longer 2
Other biology definitionOther Tags