Population Genetics


Gene diversity

Gene diversity is a measure of the expected heterozygosity in a sample of gene copies collected at a single locus. It is a summary statistic used to represent patterns of molecular diversity within a sample of gene copies. Typically, the gene copies are allelic states such as allozymes or fragment sizes (e.g., RFLPs, AFLPs, microsatellites). The expected heterozygosity is caluclated under the assumption that the sample of gene copies was drawn from a population at Hardy-Weinberg equilibrium (HWE).


Heterozygosity: An individual or population-level parameter. The proportion of loci expected to be heterozygous in an individual (ranging from 0 to 1.0).
HO (observed heterozygosity) is the observed proportion of heterozygotes, averaged over loci.
HE (expected heterozygosity) is also known as gene diversity (= D; preferred, less ambiguous term) and is calculated as 1.0 minus the sum of the squared gene frequencies. [See Weir, 1996, p. 124 for the multi-locus, multi-allele formula].
High heterozygosity means lots of genetic variability. Low heterozygosity means little genetic variability.Often, we will compare the observed level of heterozygosity to what we expect under Hardy-Weinberg equilibrium (HWE). If the observed heterozygosity is lower than expected, we seek to attribute the discrepancy to forces such as inbreeding. If heterozygosity is higher than expected, we might suspect an isolate-breaking effect (the mixing of two previously isolated populations).


A haplotype (haploid genotype) is a group of genes in an organism that are inherited together from a single parent.

Haplotype diversity (h)

Haplotype diversity is a measure of the uniqueness of a particular haplotype in a given population. The haplotype diversity (H) is computed as.

Nucleotide diversity (π)

Nucleotide diversity is a concept in molecular genetics which is used to measure the degree of polymorphism within a population.
This measure is defined as the average number of nucleotide differences per site between any two DNA sequences chosen randomly from the sample population, and is denoted by π.
Nucleotide diversity is a measure of genetic variation.
单倍型多样度(Hd)和核苷酸多样度(Pi)是衡量一个 mtDNA 变异程度的两个重要指标,Hd 值和 Pi 值越大,多样性程度越高,遗传多样性越丰富,反之,多样性程度越低,遗传多样性越贫乏。另外,
mtDNA 的单倍型多样性指数也可以衡量种内的变异程度。

更多术语见:Molecular Marker Glossary
深入学习间:Genetic Markers

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