Identify the alleles available for the trait. For example, a trait may have a total of eight alleles, 1, 2, 3, 4, 5, 6, 7 and 8, or as few as two alleles, such as L and l.
Write all the combinations of the alleles. If the alleles are 1 through 8, then start with the combination 11 and work your way to 18. Then begin the sets that have 2 in them, but leave out 12 because in genotyping no difference exists between 12 and 21. Repeat the technique for combining alleles until you make all of the combinations. As you progress through the different allele groups, the number of available combinations for each allele will decrease.
Count the total number of allele combinations, or genotypes, that you formed from the available alleles. If the available alleles for a trait are 1 through 8, then the total number of genotypes is 36 for that trait.