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An allele [1] is a variant of the sequence of nucleotides at a particular location, or locus, on a DNA molecule. [2]Alleles can differ at a single position through single nucleotide polymorphisms (SNP), [3] but they can also have insertions and deletions of up to several thousand base pairs.
Beneficial alleles tend to increase in frequency, while deleterious alleles tend to decrease in frequency. Even when an allele is selectively neutral, selection acting on nearby genes may also change its allele frequency through hitchhiking or background selection .
It has been shown that it takes only "one migrant per generation" to prevent populations from diverging due to drift. [1] Populations can diverge due to selection even when they are exchanging alleles, if the selection pressure is strong enough. [2] [3] Gene flow is an important mechanism for transferring genetic diversity among populations.
For example, often having certain alleles make an organism more susceptible to a disease than having other alleles; if an allele highly susceptible to a disease with a prevalent cause is fixed in a population, most organisms of the population might be affected.
DNA molecule 1 differs from DNA molecule 2 at a single base-pair location (a C/A polymorphism). A haplotype (haploid genotype) is a group of alleles in an organism that are inherited together from a single parent. [1] [2] Many organisms contain genetic material which is inherited from two parents.
In Mendelian inheritance, genes have only two alleles, such as a and A. Mendel consciously chose pairs of genetic traits, represented by two alleles for his inheritance experiments. In nature, such genes often exist in several different forms and are therefore said to have multiple alleles. An individual usually has only two copies of each gene ...
if the allele A frequency is denoted by the symbol p and the allele a frequency denoted by q, then p+q=1. For example, if p=0.7, then q must be 0.3. In other words, if the allele frequency of A equals 70%, the remaining 30% of the alleles must be a, because together they equal 100%. [5]
Previous research, comparing measures of dominance, overdominance and epistasis (mostly in plants), found that the majority of cases of heterozygote advantage were due to complementation (or dominance), the masking of deleterious recessive alleles by wild-type alleles, as discussed in the articles Heterosis and Complementation (genetics), but ...