Slide showing a table demonstrating a 'comparison of the mutability of the normal allelomorphs of white (Wa and Wr) in two geographical races of drosophila melanogaster'. Slide shows a table demonstrating a 'comparison of the mutability of the normal allelomorphs of white (Wa and Wr) in two geographical races of drosophila melanogaster' (fruit fly). Two adult males have been 'treated with X-ray dosage of 4800 r (Timofeeff-Ressovsky, 179)'. Headings in left column: 'Wa with "American" modifiers', 'Wa with Russina modifiers', 'Wr with Russian modifiers', 'Wr with American modifiers' and 'Wr total'. Headings in top row: 'Number of X-rayed genes', 'Number of mutations', 'Total mutations', 'Percentages W - w, of all mutations', and 'W - wx among all mutations'. Late 19th to early 20th century