Bromodeoxyuridine (BUDR) was fed to Drosophila larvae together with a thymidylate inhibitor under conditions free of larval mortality. Such treatment induces a variety of morphologic alterations in the hatching adult flies, including supernumerary structures on the wings and legs and numerous bristle defects. Wings with supernumeraries did not differ significantly in size from wings without such abnormalities, and it is thus apparent that the supernumerary structures are the result of additional growth rather than reorganization of the normal cell population of the wing during pupal metamorphosis.

BUDR dose-response relationships indicate that there is a limited number of targets which can respond as supernumeraries or single cell bristle effects on the wing. The distribution of abnormalities on the wing parallels the distribution of the underlying mesenchymal cells, and it has been postulated that the population size of these cells determines the target size.

Incorporation of BUDR in the DNA molecule is in effect mutation at the level of the genetic information. Such events at the somatic cell level would thus be somatic mutations underlying the modified growth patterns observed in the present study. This argument is further strengthened by the fact that, unlike teratogens or phenocopy agents, BUDR-5-fluorouracil treatment induces neoplastic changes which are not correlated with increased mortality, development stage specificity, or genetic strain specificity.

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