three genes as opposed to two provided most accurate information about gene order on chromosome. With this system, Sturtevant discovered that double crossing-over occurs at frequency of equal to or less than product of two single crossing over frequencies. He also surmised that unequal crossing-over was possibly a main force of evolution. "Sturtevant... elaborated on these ideas by incorporating the conception of linear arrangement and by constructing the first chromosome map. Double crossing over and interference were deductions that arose from this result" (Sturtevant, An Introduction to Genetics p. 361). Sturtevant's work on the Drosophila genome enabled geneticists to further map chromosomes of higher organisms, including human beings. His former Caltech research partner George Beadle claimed that modern biochemical genetics stems directly from Sturtevant's work. Key publications See Scholia for some of his publications. The linear arrangement of six sex-linked factors in Drosophila, as shown by their mode of association. Journal of Experimental Zoology, 14: 43–59, 1913 The North American Species of Drosophila. Carnegie Institute of Washington, 1921. A History of Genetics. Cold Spring Harbor Laboratory Press. 2001. Online Electronic Edition (originally published, New York: Harper & Row, 1965) Students Edward B. Lewis References Lewis, E.B. Alfred Henry Sturtevant, National Academy of Sciences Biographical Memoirs Sources Allan, Garland E. Isis, Vol. 66, No. 3. (Sep., 1975),pp. 332–333. Biography.com. Sturtevant, Alfred Henry. A&E Television Networks, 2007. Chromosome Map. NCBI. April 11, 2007 gi?rid=gnd.chapter.272 Definition of Chromosome Inversion. April 11, 2007. http://www.medterms.com/script/main/art.asp?articlekey=8183 Dorak MD, PhD, M. Tevfik. Landmarks in the History of Genetics. November 28, 2005. Accessed April 8, 2007. <http://www.dorak.info/genetics/notes01.html> Edelman, Isidore S. and Gerald D. Fischbach. Genes and Genomes: Impact on Medicine and Society. Genes, Genomes, and Evolution Symposium. Columbia University, 16 October 2003. Lassman, Thomas C. Government science in postwar America: Henry A. Wallace, Edward U. Condon, and the transformation of the National Bureau of Standards, 1945–1951. Isis 96.1 (March 2005): p25. Lattas, Chelsea K. Chromosome Inversions. Michigan State University. April 11, 2007 < http://www.msu.edu/~lattasch/inversion.html> Lewis, Edward B. Alfred Henry Sturtevant: November 21, 1891- April 5, 1970. Dictionary of Scientific Biography, vol. 13, pp. 133–38. New York: Chas. Scribner's Sons, 1976. Lewis, E.B., ed. Genetics and Evolution: Selected Papers of A.H. Sturtevant. San Francisco: W.H. Freeman and Company, 1961. Lorentz, Cindy Pham et al. History of Genetics and Sequencing of the Human Genome. Primer on Medical Genomics. Mayo Clinic Proceedings, August 2002, Vol 77. pp. 773–782. Provine, William B.