You and I look quite different, and neither of us looks much like a tree. Some of this difference is due to environment, but most of it is due to our "heredity"—I look more like my parents than like yours, and the attempt to understand the mechanisms of heredity is one of the great endeavors of our species. As healers of the sick, we recognize hereditary diseases and have tried to understand how such diseases might be inherited.
Classically, we approach this question influenced by Gregor Mendel, first by defining an inheritance pattern—Is this disease "passed" as an autosomal dominant, autosomal recessive, or X-linked trait? Such information can be helpful for genetic counseling, eg, for predicting the occurrence of the disease in future progeny.
For some decades now, we have tried to illuminate the mechanisms underlying hereditary diseases by shining on them the bright beams of biochemical analysis, by working
Epstein EH. Back-up Lights. Arch Dermatol. 1987;123(12):1719-1720. doi:10.1001/archderm.1987.01660360181033