Quantitative Genetics and Multifactorial Traits – Key Vocabulary

Thirty vocabulary flashcards summarizing foundational terms and concepts from the lecture on quantitative genetics and multifactorial traits.

Quantitative inheritance

A genetic phenomenon in which traits show continuous variation and are measured in quantitative terms.

Continuous variation

A range of small, incremental differences in phenotype, rather than discrete categories.

Polygenic trait

A characteristic controlled by many genes, each contributing a small additive effect to the phenotype.

Polygene

One of several genes at different loci that collectively influence a quantitative trait.

Multifactorial trait

A phenotype determined by both multiple genes and environmental influences.

Multiple-gene (multiple-factor) hypothesis

The concept that many Mendelian genes, acting additively, produce the continuous phenotypic variation seen in polygenic traits.

Additive allele

An allele that contributes a fixed, equal amount to the quantitative phenotype; the basis of cumulative effects.

Nonadditive allele

An allele that does not contribute to the additive genetic effect for a quantitative trait.

Quantitative trait locus (QTL)

A specific chromosomal region containing one or more genes that influence a quantitative trait.

Additive variance (VA)

The portion of genotypic variance attributable to the sum of average effects of individual alleles.

Dominance variance (VD)

Genotypic variance caused by interactions between alleles at the same locus when heterozygote expression deviates from additivity.

Interactive (epistatic) variance (VI)

Genotypic variance arising when alleles at different loci interact to influence phenotype.

Phenotypic variance (VP)

The total observed variation in a quantitative trait within a population.

Genotypic variance (VG)

The part of phenotypic variance that is due to genetic differences among individuals.

Environmental variance (VE)

The portion of phenotypic variance that results from environmental differences rather than genetics.

Genotype-by-environment interaction (VG×E)

Variance component arising when different genotypes respond differently to environmental conditions.

Broad-sense heritability (H2)

The proportion of total phenotypic variance that can be attributed to all genetic variance (VG/VP).

Narrow-sense heritability (h2)

The fraction of phenotypic variance due solely to additive genetic variance (VA/VP).

Heritability estimate

A numeric value (0–1) indicating the proportion of observed trait variation due to genetic factors in a specific population and environment.

Mean (arithmetic mean)

The average value of a set of measurements, serving as the central point in a distribution.

Variance

The average squared deviation of observations from the mean, describing data spread.

Standard deviation (s)

The square root of variance; about 95% of values fall within ±2s of the mean in a normal distribution.

Standard error of the mean (SEM)

An estimate of how much sample means would vary if the experiment were repeated; smaller than standard deviation.

Normal distribution

A symmetrical, bell-shaped frequency curve typical of quantitative trait data in large samples.

Artificial selection

The human practice of breeding individuals with desired phenotypes to increase those traits in future generations.

Realized heritability

The heritability value calculated from the response to artificial selection, reflecting actual breeding results.

Concordant (in twins)

A condition where both twins either express or both fail to express a given trait.

Monozygotic (MZ) twins

Identical twins arising from a single zygote, sharing (nearly) the same genotype.

Dizygotic (DZ) twins

Fraternal twins produced from two separate fertilization events, genetically similar to ordinary siblings.

Multiple-factor ratio (1:4:6:4:1)

The F2 phenotypic distribution produced when two additive gene pairs influence a trait, illustrating polygenic inheritance.