Timelines: 1902
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The chromosomal theory of genetic inheritance
Walter Sutton (left) and Theodor Boveri
Grasshoppers and sea urchins
American geneticist Walter Sutton and German biologist Theodor Boveri independently formulate evidence-based theories of chromosomal inheritance. Working with grasshoppers under the direction of prominent zoologist E.B. Wilson at Columbia University, Sutton observes that, in meiosis (cell division that produces gametes — sperm and egg cells), the number of chromosomes is halved. He proposes that “the association of paternal and maternal chromosomes in pairs and their subsequent separation … may constitute the physical basis of the Mendelian law of heredity.” Boveri’s studies of sea urchins establish that individual chromosomes carry portions of the hereditary material, not the totality, and that, in diploid organisms (those that receive chromosomes from both parents — i.e., most plants and animals), chromosome pairs are necessary for normal development.