Pattern formation in the wing and haltere imaginal discs after irradiation ofDrosophila melanogaster first instar larvae.

In order to examine pattern formation in young imaginal discs consisting of only a few cells, freshly hatched larvae were irradiated with 1500 rads of γ-rays to kill cells. When these larvae became adults, their wings and halteres were examined to find aberrant patterns. Most of the abnormal patterns consisted of mirror image duplications of structures arising from parts of the periphery of the wing disc. A second group of patterns contained most structures present once in normal orientation, but in addition, pattern elements arising from parts of the wing disc periphery were deleted. The third group of aberrant appendages contained triplication of parts of the wing. The central part of the wing disc seemed to control whether duplication or deletion was found, since duplicated patterns seldom had structure from the central part of the disc, whereas deleted patterns always contained the elements formed by the central region of the disc. It appeared that if the central region was killed leaving only some of the periphery alive, then the remaining live cells duplicated their pattern. But if the periphery was killed and the central region remained, then the disc would be either partially deleted or completely regenerated. Aberrant halteres were found which were similar to the three groups of abnormal wings, and the anterior of the haltere disc seemed to correspond to the central region of the wing disc. The results are discussed in terms of a gradient of developmental capacity with its high point in the central part of the wing disc and low points at the disc periphery.