Morphological and somatic clonal analyses of pattern triplications

The growth of pattern triplications induced by a 48-hr 29 degrees C treatment given to larvae homo- or hemizygous for a ts cell-lethal mutation was examined to determine which structures result from new, regulative growth and which are produced by the original imaginal disc cells. Pattern triplications contain one complete leg pattern (orthodrome) and two partial patterns (antidrome and paradrome). The results of two morphological analyses and one somatic clonal analysis suggest that in triplications in which the antidrome and paradrome become more complete distally (diverge) the paradrome is formed by a portion of the original leg pattern, and the antidrome and orthodrome are formed by extra, regulative growth. A different result is suggested for triplications in which the antidrome and paradrome become less complete distally (converge). In these, the orthodrome appears to be formed by the original leg pattern and the antidrome and paradrome by extra growth. These results agree with predictions based on the polar coordinate model of positional information.