According to Mendelian genetics, a trait controlled by a single gene shows segregation of 3:1 ratio in the progeny.
• A dihybrid ratio (two loci with two alleles each) gives 9 genotypes and 5 phenotypes
• A trihybrid ratio (three loci with two alleles each) gives 27 genotypes and 9 phenotypes
• If the number of loci is four with two alleles each for the loci, the possible phenotypes are 16. The progeny have a phenotypic ratio of 81:27:27:27:27:9:9:9:9:9:9:3:3:3:3:1
Therefore, for the theoretical 17 height classes, at least 5 gene loci with two alleles each are required.