Slide showing 'an experiment for the detection of lethals in the second chromosome of Drosophila melanogaster' (fruit fly). Slide shows 'an experiment for the detection of lethals in the second chromosome of Drosophila melanogaster.' The experimental data consists of three sets of diagrams labelled 'P1', 'P2' and 'F1'. The title below the data reads: 'Fig. 2 - an experiment for the detection of lethals in the second chromosome of Drosophila melanogaster. The Cy chromosome eliminates the cross-overs in the female, and usually the homozygote does not survive. Either males or females may be treated, according to this techique; the diagram illustrates an experiment in which males are treated. It should be noted that, in this experiment, use is made of two dominant marking genes (Cy and A, which may be any one of a number of different dominants).' Late 19th to early 20th century