non mendelian

Epistasis

A form of gene interaction where one gene masks, interferes with, or prevents the phenotypic expression of another gene at a different locus.

Dominant Epistasis

An interaction where a dominant allele at one locus masks the expression of alleles at a second locus, resulting in a typical $12-3-1$ $F_2$ phenotypic ratio.

Recessive Epistatis

An interaction where homozygous recessive alleles at one locus mask the expression of alleles at a second locus (e.g., Labrador or pepper coat/fruit color). - 9-3-4

Duplicate Dominant Epistasis / Redundant Genes

An interaction where a dominant allele at either of two loci produces the same phenotype, yielding a $15-1$ ratio.

Incomplete Dominance / Semidominance

A condition where neither allele is fully dominant, and the heterozygote exhibits an intermediate phenotype (e.g., red $R_1R_1$, pink $R_1R_2$, white $R_2R_2$ snapdragons).

Pleiotropy

A phenomenon where a single gene influences multiple, seemingly unrelated phenotypic traits.

Penetrance

The percentage of individuals with a specific genotype who actually express the corresponding phenotype.

Expressivity

The degree or intensity to which a given genotype is expressed phenotypically in an individual.

Polygenic / Additive Gene Action

Traits controlled by multiple genes where each gene contributes a small, additive increment to the final phenotype (e.g., wheat kernel color).