Genetics was established as a branch of biology in the early 1900's. It developed chiefly from experiments conducted during the mid-1800's by Gregor Mendel, an Austrian monk. On the basis of his experiments, Mendel discovered that physical characteristics are produced by basic hereditary units that transmit traits from generation to generation. About 1910, Thomas Hunt Morgan, an American biologist, found that Mendel's hereditary units--later called genes--are located on structures called chromosomes within cells. Biologists at the time also noted that changes in hereditary traits correspond to visible changes in chromosome structure.
During the 1940's, geneticists found that genes guide the manufacture of the proteins by which cells regulate their chemical processes. In 1953, biologist James D. Watson of the United States and physicist Francis H. C. Crick of Britain proposed a model of the molecular structure of deoxyribonucleic acid (DNA), the material in chromosomes that controls heredity. Knowing the structure of DNA enabled biologists to understand the molecular basis of many life processes, including heredity and genetic change.
Breakthroughs in genetics helped alter biologists' approach to the study of evolution. By the 1960's, many biologists were studying evolution in terms of changes in the kinds and numbers of genes in a population.
Excerpt from the "Biology" article, The World Book Encyclopedia © 1999