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An odds ratio (OR) is a statistic that quantifies the strength of the association between two events, A and B. The odds ratio is defined as the ratio of the odds of event A taking place in the presence of B, and the odds of A in the absence of B. Due to symmetry, odds ratio reciprocally calculates the ratio of the odds of B occurring in the presence of A, and the odds of B in the absence of A.
The number of loops is always the number of common ancestors the parents have. If an individual is inbred, the coefficient of inbreeding is calculated by summing all the probabilities that an individual receives the same allele from its father's side and mother's side.
Ewens's sampling formula, introduced by Warren Ewens, states that under certain conditions (specified below), if a random sample of n gametes is taken from a population and classified according to the gene at a particular locus then the probability that there are a 1 alleles represented once in the sample, and a 2 alleles represented twice, and so on, is
In population genetics, the Balding–Nichols model is a statistical description of the allele frequencies in the components of a sub-divided population. [1] With background allele frequency p the allele frequencies, in sub-populations separated by Wright's F ST F, are distributed according to independent draws from
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.
then the allele frequency is the fraction of all the occurrences i of that allele and the total number of chromosome copies across the population, i/(nN). The allele frequency is distinct from the genotype frequency, although they are related, and allele frequencies can be calculated from genotype frequencies. [1]
For example, if a population includes allele A with frequency equal to 20%, and allele a with frequency equal to 80%, there is an 80% chance that after an infinite number of generations a will be fixed at the locus (assuming genetic drift is the only operating evolutionary force).
Punnett square for three-allele case (left) and four-allele case (right). White areas are homozygotes. Colored areas are heterozygotes. Consider an extra allele frequency, r. The two-allele case is the binomial expansion of (p + q) 2, and thus the three-allele case is the trinomial expansion of (p + q + r) 2.