Disapline mostly concerned with allele frequencies to define the intraspecific (intra-species) population structure, but can be applied to phenotypic outcome, e.g. Medel's pea plants
Large and perhaps the oldest disapline in genetics stemming from Gregory Medel's work on inheritance which became the basis for the Hardy-Weinberg equiilibrium. The modern approach is to examine the frequency of alleles to define a "population", which for Mendellian eukaryotes defines a group of freely reproducing individuals. Extremely useful series of approach to define genetic migration and genetic variation, such as Fst, Fis, and linkage disequilibrium. Mathematically, it is a very different approach to phylogenetics.