Complementation test for genetic mapping of hypnos-2^P. The hypnos-2^P mutation was located previously between genetic markers y (1B1) and cv (5B) on the X chromosome (10). To further map the cytological location of hypnos-2^P mutation, genetic crosses between hypnos-2^P flies and other deficiencies in this region were carried out (a). The recovery time after 5-minute anoxia was significantly prolonged in the hypnos-2^P–mutant flies when compared with either its heterozygotes (hypnos-2^P/+) or control (C-S) flies (P < 0.0001). The average recovery time (mean ± SE) for hypnos-2^P, heterozygote (hypnos-2^P/+), and C-S is 615.8 ± 23.5 seconds (n = 58), 321.1 ± 7 seconds (n = 51), and 324 ± 5.8 seconds (n = 204), respectively. Since the heterozygote female flies (hypnos-2^P/+) have a distribution similar to that of the wild-type flies, this mutation is recessive. It should be noted that there are two alleles at the hypnos-2 locus (hypnos-2^L and hypnos-2^P), but we have focused on hypnos-2^P in this work. Our studies showed that hypnos-2^P flies failed to complement with the deletions of either df(1)A94 (1E3-2B15) or df(1)st472 (2B6-2B12), but they complemented with df(1)S39 (1E1-2B5). ^AP < 0.0001. (b) Schematic presentation of cytological locations of three deficiencies used in the complementation tests. The results from these complementation tests indicate that the hypnos-2^P mutation is located in the region between 2B6 and 2B12 on the X chromosome.