Slide showing a table of 'frequency of mutation at different loci in the X chromosome of Drosophila Melanogaster' (fruit fly). Slide shows a table of 'frequency of mutation at different loci in the X chromosome of Drosophila Melanogaster'. The title of the table is 'Table 2 - Frequency of mutation at different loci in the X chromosome of Drosophila Melanogaster'. There are five columns. Column 1 is headed 'locus', and there are ten rows indicated by lower case letters. Column 2 is headed 'tested chromosones' which are indicated by numbers in tens of thousands. Column 3 is headed 'number of mutations'. Column 4 is headed 'X-ray treatment', and column 5 is headed 'authority', in which names of the relevant researchers are quoted. Late 19th to early 20th century