Comparison Note — Incomplete Dominance vs Co-dominance vs Multiple Alleles — Notes

Feature	Incomplete Dominance	Co-dominance	Multiple Alleles
Definition	Neither allele fully dominant; heterozygote shows intermediate phenotype	Both alleles fully and simultaneously expressed in heterozygote	More than 2 allelic forms of a gene exist in a population
Heterozygote phenotype	Blended intermediate (e.g., pink)	Both parental phenotypes present (e.g., both A and B antigens)	Depends on which two alleles are present
F2 phenotypic ratio	1:2:1 (= genotypic ratio)	1:2:1 (= genotypic ratio)	Varies by cross
Classic NEET example	Snapdragon flowers: Red (RR) × White (rr) → Pink (Rr)	ABO blood group: $I^A$ $I^B$ → Blood group AB	ABO system: $I^A$ , $I^B$ , i (3 alleles in population)
Molecular basis	Haploinsufficiency — one allele makes insufficient product	Both alleles make independent, complete products	Multiple structural variants of the same gene
Number of alleles/individual	2	2	2 (but >2 in population)
Violates Law of Dominance?	Yes — neither allele is "dominant"	Yes — both alleles are co-dominant	Partly — $I^A$ and $I^B$ co-dominant; both > i
Does segregation still occur?	Yes — Rr gametes separate into R and r normally	Yes — $I^A$ $I^B$ gametes separate into $I^A$ and $I^B$	Yes — any two alleles separate normally

Pink snapdragons = incomplete dominance (blended phenotype)
AB blood group = co-dominance (both antigens present, not blended)
"3 alleles for ABO in population" = multiple allelism (not the same as an individual having 3 alleles)