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In population genetics, a fixed allele is an allele that is the only variant that exists for that gene in a population. A fixed allele is homozygous for all members of the population. [1] The process by which alleles become fixed is called fixation. For this hypothetical species, the population in the topmost frame exhibits no fixed allele for ...
In the process of substitution, a previously non-existent allele arises by mutation and undergoes fixation by spreading through the population by random genetic drift or positive selection. Once the frequency of the allele is at 100%, i.e. being the only gene variant present in any member, it is said to be "fixed" in the population. [1]
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 .
[7] [8] XCI is a chromosome-wide monoallelic expression, that includes expression of all genes that are located on X chromosome, in contrast to autosomal RME (aRME) that relates to single genes that are interspersed over the genome. aRME's can be fixed [9] or dynamic, depending whether or not the allele-specific expression is conserved in ...
(of a gene or allele) Traceable back through an arbitrary number of generations without mutation to a common ancestor of the group of descendant organisms that carries the gene or allele. [1] A gene or allele present in a group of descendant organisms is said to be identical by descent to a gene or allele in a common ancestor of the group if ...
The Hardy–Weinberg law describes the relationship between allele and genotype frequencies when a population is not evolving. Let's examine the Hardy–Weinberg equation using the population of four-o'clock plants that we considered above: if the allele A frequency is denoted by the symbol p and the allele a frequency denoted by q, then p+q=1.
A highly indicative test of changes in allele frequencies is the QTL sign test, and other tests include the Ka/Ks ratio test and the relative rate test. The QTL sign test compares the number of antagonistic QTL to a neutral model, and allows for testing of directional selection against genetic drift. [11]
If ¯ is the average frequency of an allele in the total population, is the variance in the frequency of the allele among different subpopulations, weighted by the sizes of the subpopulations, and is the variance of the allelic state in the total population, F ST is defined as [2]