Additive Gene Action: Associated Phenomena

Correct Answer: Additive Gene Action

From the notes: Polygenic inheritance, GCA, and resemblance between relatives are all due to Additive Gene Action (AGA).

What is Additive Gene Action?

Each allele at multiple loci contributes a small, equal, and cumulative (additive) effect to the phenotype. Example from notes: If AA = 10 and aa = 0, then Aa = 5 → each 'A' allele adds exactly 2.5 units.

All Phenomena Governed by AGA (from notes)

• Polygenic traits (multiple genes, one character)
• General Combining Ability (GCA) — average performance across all crosses
• Resemblance between relatives (chief determiner)
• Response to individual selection and pedigree selection
• Heritability in narrow sense (VA/VP)

Contrast with NAGA

Non-additive gene action (NAGA) → Heterosis, SCA, allelic interactions (dominance, over-dominance), non-allelic interactions (epistasis).