10 women who made major contributions to the fields of microbiology and genetics are recognized. Rosalind Franklin provided key evidence for the structure of DNA. Nettie Stevens supported her hypothesis that a fetus’s sex was determined by chromosomes, not environment. Barbara McClintock discovered mobile genetic elements. Salome Gluecksohn Waelsch founded the field of developmental genetics. Esther Lederberg discovered the lambda phage, worked on the F fertility factor, and, developed the method of replica plating. One theme throughout this episode is how little credit these women recieved for their work.