Cytogenetic localisation of the purine 1 and guanosine 1 loci of Drosophila melanogaster; the purine 1 locus specifies a vital function.

Three auxotrophic mutants at two loci (pur 1 and gua 1) apparently involved in purine metabolism were mapped cytologically to region 9E1-9E3 on the X-chromosome of Drosophila. Because mutants of pur 1 behaved as semi-lethals against deficiencies even on permissive medium, it appears that the pur 1 locus is vital to the fly and its auxotrophic mutants are hypomorphs.