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:2/21/2017)... and PORTLAND, Ore. , Feb. 22, ... Avamere Family of Companies (Avamere Health Services, Infinity Rehab, ... six-month research study that will apply the power of ... senior living and health centers. By analyzing data streaming ... gain insights into physical and environmental conditions, and obtain ...
(Date:2/14/2017)... 2017  Wake Forest Baptist Medical Center today announced Julie ... executive officer (CEO). Freischlag joins the medical center on ... , M.D., who last year announced that he would ... after leading it since 2008.   As ... Forest Baptist,s academic health system, which includes Wake Forest ...
(Date:2/10/2017)... 2017 Research and Markets has ... Medicine - Scientific and Commercial Aspects" to their offering. ... ... integrated with therapy for selection of treatment as well for ... prevention of disease in modern medicine. Biochip/microarray technologies and next ...
Breaking Biology News(10 mins):
Other biology definition