A Fate Map of Larval Organs of Drosophila and Preblastoderm Determination

Abstract

The construction of embryonic fate maps in Drosophila that locate the foci at which genes exert their primary effects¹ has been extended successfully to internal organs involved in behavioural characters². Essentially the mapping is based on analysis of frequencies of disagreements (expressed as Sturt units) in the genotype of pairs of organs in genetic mosaics. The rationale of the mapping procedure is that “the farther apart any two blastoderm sites are, the greater the probability that the randomly oriented boundary in a mosaic blastula will pass between them”². Cleavage divisions produce in Drosophila an internal cluster of nuclei, the relative position of which tends to be maintained during their migration to the surface blastoderm. Since it is assumed that the site at which a nucleus lands at the surface decides its fate, the fate map is considered to be a map of blastoderm potentials. The good agreement between the location of foci of behavioural characters obtained by the genetic method and by direct embryological inferences² stresses the reliability of this mapping procedure.