November 21, 1981: American Geneticist Alfred Henry Sturtevant was Born
Alfred Henry Sturtevant (November 21, 1891 – April 5, 1970) was an American geneticists who in 1913 developed a technique for mapping the location of specific genes of the chromosomes in the fruit fly Drosophila. Sturtevant further introduced the concept of locus into genetic study base on the technique.
Reference
https://global.britannica.com/biography/Alfred-Henry-Sturtevant
Image Source
http://biologia.uab.es/genetica/curso/EnsayosAlumnos/MeiVentura/GENETICA/personatges.htm