ADDITIVE GENETIC VARIATION The genetic variation that can be statistically associated with the effects of genes that are independent of other loci or alleles. This is the component of variance that contributes to the response to selection.
ALLOZYME LOCI Loci that code for different electrophoretic forms of the same enzyme as a result of allelic differences.
COMPLEX CHARACTERS Traits that are determined by many genes, almost always interacting with environmental influences.
CROSS-FOSTERING Transplantation of some progeny from a biological mother to an unrelated foster mother. Under this design, all resemblance among unrelated individuals reared by the same mother are ascribed to a common rearing environment, eliminating genetic effects.
EVOLUTIONARY TRADE-OFF This occurs when the evolution of one trait is limited by the evolution of an associated trait in the opposite direction or because of negative genetic correlations. Trade-offs limit the number of traits that can be maximized simultaneously through evolutionary responses to selection.
EVOLUTIONARY TRAJECTORY The expected direction of evolutionary change in a trait over time. In adaptive evolution, the trait is expected to evolve towards an adaptive peak, or point of maximum fitness for the population.
FUNCTIONAL INTEGRATION Traits that together form a functional unit or character, such as the anatomical regions of the skull. Such traits are expected to have experienced stabilizing selection that favours functionally compatible trait values.
GAME-THEORY PREDICTION A model that investigates phenotypic evolution, particularly behaviour, when the fitness of the phenotypes depends on their frequency in the population.
GENETIC CORRELATION The correlation between traits that is caused by genetic as opposed to environmental factors. Genetic correlations are the standardized measures of genetic covariation and can take on values between +1 and -1. A genetic correlation results between two traits if the same gene affects both traits (pleiotropy) or if genes that affect the two traits are in linkage disequilibrium.
HAPLODIPLOID SPECIES Species in which males develop from haploid (unfertilized) eggs, and therefore have only a single set of chromosomes contributed by the female. Females develop from fertilized eggs that have a full complement of chromosome pairs, one from each parent.
HERITABILITY The proportion of the total phenotypic variation in a trait that can be attributed to additive genetic effects. Heritabilities are standardized measures, taking on values from zero (no genetic variation contributing to phenotypic variation in the population) to one (all of the variation in the population reflects genetic differences).
KIN SELECTION The selection that results from a behaviour or trait that contributes not only directly to the fitness of the organism, but also indirectly (that is, enhancing an individuals fitness by increasing the reproduction of a relative beyond that which could be achieved without the assistance of the relative).
LIFE-HISTORY CHARACTERS Traits that are associated with survival or reproduction of an individual, such as longevity, reproductive output, size and growth.
LOD SCORE (Base 10 'logarithm of the odds' or 'log-odds'). A method of hypothesis testing that uses the logarithm of the ratio between likelihoods under the null and alternative hypotheses.
MARKOV CHAIN MONTE CARLO APPROACH A computational technique for the efficient numerical calculation of likelihoods.
OPTIMALITY MODEL A quantitative evolutionary model that defines the maximum (or minimum) fitness values for a given trait under specified constraints. They are often used to investigate life-history evolution.
PHILOPATRIC SPECIES Those that remain in the same geographical location as at their birth.
POLYGYNY Multiple mating by males, such that families consist of both full-sibs (having the same mother and father) and half-sibs (siblings with the same mother but different fathers).
SEXUAL CONFLICT The evolution of phenotypic characteristics by sexual selection, when the trait confers a fitness benefit to one sex but a fitness cost to the other.
SEXUAL SELECTION The selection that results from differential mating success. It includes competition for mates (usually among males) and mate choice (usually by females).
VARIANCE A statistic that quantifies the dispersion of data about the mean. In quantitative genetics, the phenotypic variance (Vp) is the observed variation of a trait in a population. Vp can be partitioned into components, owing to genetic variance (Vg), environmental variance (Ve) and gene-by-environment correlations and interactions.
