Two crucial approaches in contemporary developmental and evolutionary genetics

Relationships among genes, not individual alleles, are basic units of developmental information, targets of inheritance and selection. The smallest functional combination of an allele is the ratio with other alleles in a polygenic system, and amount of homo- and heterozygous relationships could determine especially the development of quantitative characters, as well as their adaptive response to natural selection, without changing the basic structure of a population. 
During last century biologists, and especially population geneticists, paid their full attention to the studies of individual variability in natural and laboratory conditions, answering the questions about its amounts, causes and significance. The explanations why and how individuals within a species are so much alike  to each other, i.e. what are the origins of these adaptive similarities, had been in a good part  neglected.