Traits

Qualitative trait

Phenotypic variation that is distinct and discontinuous, separated into discrete classes. Simple relationship to phenotype, you have it or not.

Quantitative trait

Phenotypic variation that is continuous and cannot be separated into discrete classes. No clear relationship to phenotype, Range of response.

Phenotypic variation

Variation in observable traits in a population, which can be classified as qualitative or quantitative.

Heritable variation

Variation in phenotype that is transmitted to progeny and influenced by genetic factors.

Environmental variation

Variation in phenotype due to differences in the environment where the organism is grown.

Heritability (h^2)

The proportion of observed variation in a progeny that is inherited, influenced by genetic and environmental factors.

Variance (V)

The dispersion of observations in a population, indicating how much a trait varies.

Phenotypic variance (VP)

The total variance observed in phenotypic traits within a population, calculated as VP = VG + VE + VGxE.

Genotypic variance (VG)

The portion of variance in phenotypic traits that can be attributed to genetic differences, calculated as VG = VA + VD + VI.

Additive Variance (VA)

The portion of genotypic variance that contributes additively to the phenotype, based on the effects of individual alleles.

Dominant Variance (VD)

The portion of genotypic variance due to the effects of dominant alleles.

Epistatic Variance (VI)

The portion of genotypic variance that results from interactions between different genes.

Gene for gene theory

The principle that for every gene that confers susceptibility to a disease, there is an equal and opposite gene providing resistance.

Normal distribution

A statistical distribution where most observations cluster around the mean, with fewer observations appearing as you move away from the mean.