SEXUAL HOMOLOGIES AND INTERCALATION BETWEEN PARTS OF THE MALE AND FEMALE GENITAL DISKS OF DROSOPHILA-MELANOGASTER

To compare the homologies in distribution of positional values within the male and female genital discs, bilaterally symmetrical (horizontally cut) fragments were isolated and combined by mixing them together with tungsten needles. The combinations were then cultured in adult hosts before transfer to larvae for metamorphosis. Fragments that showed no regeneration when cultured intact or when mixed with identical fragments could be induced to regenerate by mixing them with different parts of the same disc. Fragments that showed occasional regeneration in controls were induced to regenerate at higher frequencies in such mixtures. Regeneration could also be induced or increased in frequency by mixing with certain fragments of the genital disc of the opposite sex. It is argued that the extra cases of regeneration in the mixed combinations are due to intercalation between the two components in the combination, and a detailed model is presented to account for the results. It is suggested that the male and female genital discs begin development with identical arrays of positional information, but that different parts of the field grow in the two sexes. The part which does not grow might be retained in the disc to provide a continuous field of positional information, although it would not produce any adult derivatives. © 1979.