Classical Genetics

Classical genetics refers to "garden experiments" in patterns of heredity and is how the field of genetics began.

In classical genetics no molecular methods are required. You work with easily observable phenotypes and, to a degree, control the crosses that occur. Classical genetics developed a powerful framework of logic that allowed mechanisms of inheritance and gene interactions, that were not directly observable at the time, to be inferred to exist.

The concepts of genotype, phenotype, true breeding "parental" lines, F₁ and F₂ crosses, Mendel's laws, and tools such as the Punnet square are used in classical genetics. This is also where definitions of dominance, zygosity, complementation, and epistatic interactions originate.

Moving into more modern classical genetics the field developed linkage mapping, test crosses, non-disjunction, and how these related to meiosis and a gene's physical location on a chromosome.

Forward Genetics isolates or creates mutants of a certain phenotype class (a Genetic Screen), organizes them into genes by complementation crosses, and determines their position on a chromosome by linkage mapping. This can also include molecular techniques like Positional Cloning. Interactions between gene products can also be inferred by epistatic interactions. (In contrast, Reverse Genetics starts with a gene sequence---and is considered a molecular genetic approach---and moves out to a phenotype.)