How to Calculate Allele Frequencies
If an STR locus had only one allele, it would be present in all the elephants in a population, making its frequency 100% or 1.0. For loci with more than one allele, the sum of all the allele frequencies will always be 1.0. Frequencies are determined by how many individuals in a population have each allele, taking into consideration that each diploid individual can carry either one or two copies of a particular allele for any genetic marker. As you will learn in Case Two, scientists have collected many DNA samples from different populations of African elephants and determined the genetic profiles of those samples. The data have allowed them to calculate allele frequencies in each population.
In this case, the truck containing the tusks was found in an area that is equally near three national parks, so the frequencies of the alleles in the ivory sample were determined by calculating how many times each allele is present in samples collected from those three populations.