Useful Mechanics for Mendelian analysis (assuming unlinked loci)
n = number of segregating loci
e.g. consider an AaBb individual: 2 loci.
2n = number of kinds of gametes formed by the F1 hybrid
22 = 4 (AB, Ab, aB,ab)
2n = number of F2 phenotypes if there is complete dominance at
each locus; also gives number of phenotypes and genotypes in testcross progeny
22 = 4 phenotypic classes (e.g. 9:3:3:1); (AaBb, Aabb, aaBb,aabb)
3n = number of F2 genotypes, or, the number of F2 phenotypes if
there is incomplete dominance at each locus.
32 = 9 genotypes (e.g. AABB: AABb, AAbb, AaBB, AaBb, Aabb, aaBB,
aaBb, aabb)
4n = number of possible combinations of F1 gametes, or, the number
of possible F2 genotypic combinations
42 = 16 (e.g. number of cells in the F2 Punnett square)