June 13, 1926: French Pediatrician and Geneticist Jérôme Lejeune Born
Jérôme Lejeune (June 13, 1926 – April, 3 1994) was a French pediatrician and geneticist. Dr. Lejeune proved that chromosome abnormalities are related to inherited diseases, and discovered that Down syndrome was caused by having three copies of the genes on chromosome 21.
Reference
http://www.independent.co.uk/news/people/obituary-professor-jerome-lejeune-1369490.html
Image Source
https://en.wikipedia.org/wiki/Jérôme_Lejeune