Genetic Evidence of a Selective Segregation of Chromosomes in Sciara (Diptera).

This shows that miniature-a mutates to wild type at the formation of germ cells in miniature-a males and heterozygous and homozygous females. Miniature-a mutates to wild type in somatic cells as well. Mosaic flies having part of the wing miniature and the other part wild type are very frequent and are easily distinguished. If miniature-a wings are examined under high magnification almost all of them show small areas of wild-type tissue. The Frequency of Mutations.-The frequency of mutations of miniaturea to wild type can be changed by selection. Selection made for low frequency gave a practically constant miniature line, and selection for high frequency of mutation resulted in a line in which over 70 per cent of flies from miniature-a parents were wild type. Discussion.-In its general behavior miniature-a can be compared with well-known, frequently mutating genes in plants which produce chlorophyll and anthocyan variegations. On the other hand, it differs strikingly from the gene for "reddish" (mentioned above) because it mutates in all stages of development. (The mutating period of reddish is strictly limited to the maturation division of heterozygous females.) 1 Demerec, M., these PROCEEDINGS, 12, 1926 (11-16).