ABC
See approximate Bayesian computation.

acrocentric
Chromosomes and chromatids with a centromere near one end.

addition rule
See sum rule.

additive genetic variation
The portion of total genetic variation that is the average effect of substituting one allele, responsible for a phenotypic trait, for another. The proportion of genetic variation that responds to natural selection.

admixture
The formation of novel genetic combinations through hybridization of genetically distinct groups.

AFLP
See amplified fragment length polymorphism.

agamospermy
The asexual formation of seeds without fertilization in which mitotic division is sometimes stimulated by male gametes.

alien species
A non-native or nonindigenous species.

allele
Alternative form of a gene.

allelic diversity
A measure of genetic diversity based on the average number of alleles per locus present in a population.

allelic richness
A measure of the number of alleles per locus; allows comparison between samples of different sizes by using various statistical techniques (e.g., rarefaction).

allopatric
Species or populations that occur in geographically separate areas.

allopolyploid
A polyploid originating through the addition of unlike chromosome sets, often in conjunction with hybridization between two species.

allozygous
An individual whose alleles at a locus are descended from different ancestral alleles in the base population. Allozygotes may be either homozygous or heterozygous in state at this locus.

allozyme
An allelic enzyme detected through protein electrophoresis used in many genetic applications such as hybrid identification and estimation of genetic variation.

AMOVA
See analysis of molecular variation.

amplified fragment length polymorphism (AFLP)
A technique that uses PCR to amplify genomic DNA, cleaved by restriction enzymes, in order to generate DNA fingerprints; it is a combination of RFLP and arbitrary primer PCR. It does not require prior sequence knowledge.

amplify
To use PCR to make many copies of a segment of DNA.

anagenesis
Evolutionary changes that occur within a single lineage through time. See cladogenesis.

analysis of molecular variation (AMOVA)
A statistical approach to partition the total genetic variation in a species into components within and among populations or groups at different levels of hierarchical subdivision. Analogous to ANOVA in statistics.

aneuploid
A chromosomal condition resulting from either an excess or deficit of a chromosome or chromosomes so that the chromosome number is not an exact multiple of the typical haploid set in the species.

anneal
The joining of single strands of DNA because of the pairing of complementary bases. In PCR, primers anneal to complementary target DNA sequences during cooling of the DNA (after DNA is made single stranded by heating).

ANOVA
Analysis of variance.

apomixis
Seed development without fertilization and meiosis. An apomict or apomictic plant produces seeds that are genetically identical to the parent plant.

approximate Bayesian computation (ABC)
A statistical framework using simulation modeling to approximate the Bayesian posterior distribution of parameters of interest (e.g., Ne, Nm) often by using multiple summary statistics (He, number of alleles, FST). It is far faster computationally than fully Bayesian approaches but generally slightly less accurate and precise.

artificial selection
Anthropogenic selection of phenotypes, with a heritable genetic basis, to elicit a desired phenotypic change in succeeding generations.

ascertainment bias
Selection of loci for marker development (e.g., SNPs or microsatellites) from an unrepresentative sample of individuals, or using a particular method, which yields loci that are not representative of the spectrum of allele frequencies in a population. For example, the choice of loci with high heterozygosity may bias assessments of allele frequency distributions in future studies using the loci such that alleles at low frequency (rare alleles) are underrepresented.

assignment tests
A statistical method using multilocus genotypes to assign individuals to the population from which they most likely originated (i.e., in which their expected multilocus genotype frequency is highest).

associative overdominance
An increase in fitness of heterozygotes at a neutral locus because it is in gametic disequilibrium at a locus that is under selection. Also known as pseudo-overdominance. Compare with hitchhiking.

assortative mating
Preferential mating between individuals with a similar (or a different) phenotype is referred to positive (or negative) assortative mating. See also disassortative mating.

autogamy
Self-fertilization in a hermaphroditic species where the two gametes fused in fertilization come from the same individual.

autosomal
A locus that is located on an autosome (i.e., not on a sex chromosome).

autosomes
Chromosomes that do not differ between sexes.

autozygosity
A measure of the expected homozygosity where alleles are identical by descent.

autozygous
Individuals whose alleles at a locus are identical by descent from the same ancestral allele.