Medical Genetics If a second locus, called the tall locus or t, is also involved in height, with three alleles as above, one adding two inches, one neither adding nor subtracting from the phenotype, and one subtracting 2 inches, with the neutral allele occurring twice as frequently as the either of the others, the histogram becomesMedical Genetics If a second locus, called the tall locus, or t, is also involved in height, with three alleles as above, one adding two inches, one neither adding nor subtracting from the phenotype, and one subtracting 2 inches, with the neutral allele occurring twice as frequently as the either of the others, the histogram becomes: