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

'"/>


See more about: Allele frequency

TAG: Allele frequency
Other biology definition
(Date:8/19/2008)...versity of Oklahoma researchers began studying the...that has plagued the energy industry for decades, ...ity of microorganisms capable of converting hydroc...d that the groundbreaking processknown as anaerobi...ethane gas production from older, more mature oil ...
(Date:8/19/2008)...ften goes undetected can block the lung,s natural ...ng to researchers at National Jewish Health. The f...o appear in the October issue of Infection and Im...ers to develop chronic obstructive pulmonary disea...e of chronic obstructive pulmonary disease (COPD),...
(Date:8/19/2008)... 18, 2008 With oil prices skyrocketing, the searc...search published this month in Agronomy Journal ... , Corn stover is made up of the leaves and stal... harvesting the edible corn grain. Corn stover cou...d by 2030. , Scientists with the USDA-ARS Agroe...
(Date:8/19/2008)...beyond the advice to drink enough H2O and not eat ...ental with grapefruit, onions, peppers, tomatoes, ...Chemical Society meeting., The world,s largest s... of its Agricultural and Food Chemistry Division w...the health benefits from phytochemicals in fruits ...
Breaking Biology News(10 mins):OU researchers isolate microorganisms that convert hydrocarbons to natural gas 2OU researchers isolate microorganisms that convert hydrocarbons to natural gas 3Infection blocks lung's protective response against tobacco smoke 2Clemson physicist addresses international forum on thermoelectric energy 664 1Clemson physicist addresses international forum on thermoelectric energy 664 2Researchers 3A No faking it crocodile tears are real 662 1Researchers 3A No faking it crocodile tears are real 662 2Inverness Medical Innovations Acquires Bio Stat Healthcare Group 2787 1Inverness Medical Innovations Acquires Bio Stat Healthcare Group 2787 2SEIU Launches Ad Campaign Opposing Corporate Raiders Plan to Buy Mich Nursing Homes 2782 1SEIU Launches Ad Campaign Opposing Corporate Raiders Plan to Buy Mich Nursing Homes 2782 2
...g could be used as an early warning system to dete...published in the British Ecological Society,s Jour...evious research has focused on bird song and vocal...ole played by habitat loss and fragmentation on so...e songs of more than 200 Dupont,s larks, Chersophi...
...Grant researchers have isolated a new peptide anti...ications for managing many diseases in oysters. , ...ensin" (AOD) may protect against bacteria in Crass...h Carolina and important economically to Atlantic ...helpful in selecting disease-resistant oysters for...
... professor of chemical engineering at the Universi...hortcomings of injections have led to active resea...nization. , While most people prefer to avoid inj...t helping people avoid a disagreeable prick of a n...fe use of the needles used in injections causes mi...
...llows a dynamic pattern, allowing for retrieval fr... an organism needs to remember, said a researcher ...Ron L. Davis, professor of molecular and cellular ...t report on the topic that finds a memory trace in...neurons called the dorsal pair medial neurons, but...
Other Biology News:Pregnancy drugs can affect grandkids 2Tracking the memory trace 2