[motion picture] Points out how the differences in characteristics in animals and plants have always interested man and have led to Mendel's experiments with peas and today's experiments with Drosophila. Uses animation to picture Mendel and his basic discoveries of inheritance. Stresses advantages of Drosophila in studying genetics and uses macrocinematography to illustrate mutations which may be produced with X-rays. Shows Dr. H. J. Muller at work in his laboratory at Indiana University X-raying fruit flies. Dr. Sonneborn experimentally reveals the role the cytoplasm plays in inheritance by mixing different strains of paramecia. Views model of DNA and points out that how it is joined and reproduces itself is a problem for future experimenters to uncover.