HAPLOIDY AND ANDROGENESIS IN DROSOPHILA

Androgenesis, development from paternal but not maternal chromosomes, can be induced to occur in some organisms, including vertebrates, but has only been reported to occur naturally in interspecific hybrids of the Sicilian stick insect. Androgenesis has not been described previou sly in Drosophila. We now report the recovery of androgenetic offsprin g from Drosophila melanogaster females mutant for a gene that affects an oocyte- and embryo-specific alpha-tubulin. The androgenetic excepti ons are X,X diploid females that develop from haploid embryos and expr ess paternal markers on all 4 chromosomes. The exceptional females ari se by fusion of haploid cleavage nuclei or failure of newly replicated haploid chromosomes to segregate, rather than fusion of two inseminat ing sperm. The frequency of androgenetic offspring is greatly enhanced by a partial loss-of-function mutant of the NCD (nonclaret disjunctio nal) microtubule motor protein, suggesting that wild-tgpe NCD function s in pronuclear fusion. Diploidization of haploid paternal chromosome complements results in complete genetic homozygosity, which could faci litate studies of gene variation and mutational load in populations.