So far in this course we've dealt only with variation at a single locus. There are obviously many traits that are governed by more than a single locus in whose evolution we might be interested. And for those who are concerned with the use of genetic data for forensic purposes, you'll know that forensic use of genetic data involves genotype information from multiple loci. I won't be discussing quantitative genetic variation for a few weeks, and I'm not going to say anything about how population genetics gets applied to forensic analyses, but I do want to introduce some basic principles of multilocus population genetics that are relevant to our discussions of the genetic structure of populations before moving on to the next topic. To keep things relatively simple multilocus population genetics will, for purposes of this lecture, mean two-locus population genetics.