Slide showing two diagrams of the 'translocation between 'x' and 'y' chromosome ('y' with male fertility factor)' of the fruit fly. Slide shows two diagrams of the 'translocation between 'x' and 'y' chromosome ('y' with male fertility factor)' of the fruit fly. Title above diagrams reads: 'translocation between 'x' and 'y' chromosome ('y' with male fertility factor)'. Diagrams are labelled 'p' and 'f1'. Title below image reads: 'Fig 19. - two strains of Drosophila melanogaster that produce sterile male hybrids when crossed. X - chromosome, stippled; Y- chromosome, dotted. Upper left, normal female; upper right, male from the translocation strain; below, the hybrids. F, fertile; ST, sterile. (From Stern).' Late 19th to early 20th century