Table 1.

Definitions of complex phenomena in population genetics and dynamics and their homologues from epidemiology

TermPopulation geneticist's explanation
ApomorphismDerived character state.
CladisticsPhylogenetic method relying on the distinction of ancestral and derived character states. Only those derived characters that are shared by distinct lines (synapomorphic characters) convey reliable information. This contrasts with the value of symplesiomorphic characters (shared ancestral characters) and autapomorphic characters (characters owned by a single, unique line).
ClonetAll the individuals of a clonal species that have a similar profile for a particular set of genetic markers.
ConvergencePossession of the same character by different lines through convergent evolution. The characters were derived from different ancestors.
EcotypeGroup of genotypes adapted to a particular niche.
DivergenceIndependent evolution by lines with a common ancestor but isolated evolutionary histories.
FitnessThe performance of a genotype or phenotype in a particular environment in terms of survival and fecundity; the expected number of offspring produced in a particular environment.
Frequency-dependent selectionThe frequency of a type of organism in the population relative to other variants; can be negative (high fitness when rare) or positive (high fitness when common).
Genetic driftThe process of random sampling of alleles for each generation, which is relatively important in small populations, and is an alternative evolutionary force for natural selection causing allele frequencies to change.
HeterozygoteIn a polyploid organism, copies of a given gene are nonidentical.
HomoplasyThe same characters are shared by several lines but are not due to common ancestry. This can be due to convergent or parallel evolution or reversion.
HomozygoteIn a polyploid organism, copies of a given gene are identical.
LineageGroup of isolates sharing essential characters due to common descent.
Linkage disequilibriumNonrandom reassortment of alleles occurring at different loci due to physical linkage. Lack or inhibition of recombination leads to linkage disequilibrium, which implies that in clonal organisms linkage disequilibrium is strong whereas in freely recombining populations there is no apparent linkage disequilibrium.
PanmixiaSituation in which gene exchange occurs randomly and at a high rate in the population.
ParallelismPossession of the same character by different lines generated independently, derived from identical ancestral characters.
PhylogenyDevelopment of systems based on evolutionary relationships rather than general resemblance (phylon: race or tribe; genesis: generation or origin).
PlesiomorphismAncestral character state.
ReversionRestoration of an ancestral character from a derived one by reversed mutation.
SynapomorphismDerived characters shared by several distinct lines.
TaxonomyTheoretical study of organism classification, which involves the clustering of units into groups; identification and development of coherent nomenclature are essential.