1930
	R. A. Fisher publishes Genetical Theory of Natural Selection, a formal analysis of the mathematics of selection.	1930
	C. Stern, and independently H. B. Creighton and B. McClintock, provide the cytological proof of crossing over.	1931
		1932
	T. S. Painter initiates cytogenetic studies on the salivary gland chromosomes of Drosophila. B. McClintock demonstrates in maize that a single exchange within the inversion loop of a paracentric inversion heterozygote generates an acentric and a dicentric chromatid. T. H. Morgan receives a Nobel Prize in Medicine for his development of the theory of the gene. He is the first geneticist to receive this award.	1933	Franklin D. Roosevelt becomes thirty-second president of the United States.
		1934
	J. B. S. Haldane is the first to calculate the spontaneous mutation frequency of a human gene. G. W. Beadle and B. Ephrussi and A. Kuhn and A. Butenandt work out the biochemical genetics of eye-pigment synthesis in Drosophila and Ephestia, respectively. C. B. Bridges publishes the salivary gland chromosome maps for Drosophila melanogaster.	1935
	A. H. Sturtevant and T. Dobzhansky publish the first account of the use of inversions in constructing a chromosomal phylogenetic tree.	1936
	T. Dobzhansky publishes Genetics and the Origin of Species - a milestone in evolutionary genetics.	1937
		1938
	E. L. Ellis and M. Delbrück perform studies on coliphage growth that mark the beginning of modem phage work. They devise the "one-step growth" experiment, which demonstrates that after the phage adsorbs onto the bacterium, it replicates within the bacterium during the "latent period," and finally the progeny are released in a "burst."	1939
		1940