Correlations between Chromosome Segments and Fitness in Drosophzla Melanogaster

Unmarked segments within the X chromosomes of four different Drosophila melanogaster isogenic lines were assessed with respect to egg-toadult viability. The results were compared with those of an earlier study involving egg production. All segments influence both traits, but to extents that are dependent upon the strains being compared. Segmental effects are also a function of the genetical background, which, in this case, constitutes material within the same chromowme. With respect to both traits, the segments are not necessarily parallel in their effects. A segment that increases fecundity, for example, may or may not augment viability. The possibility of manipulating chromosomal segments to improve “yield” in organisms is explored. N the first article in this series (CHAPCO 1977), the effects on egg production I of X-chromosome segments from four Drosophila melanogaster isogenic lines were investigated. Based on measurements involving crosses among original and derived recombinant lines, it was shown that all segments influence fecundity, but to extents which depend on strain and genetical background. In the present study another component of fitness, egg-to-adult survival, is examined with respect to the same segments. Viability measurements are based on the eggs which were counted for the earlier report. Egg-to-adult survival, along with components such as egg hatchability and larval survival, is to a very large extent maternally inherited ( STURTEVANT and BEADLE 1936; BATEMAN 1962; CHAPCO 1965; KEARSEY ~ ~ ~ K O J I M A 1967). These authors differ, however, with respect to the relative magnitude of nonmaternal effects (genotype o i the egg, egg-sperm incompatibility, etc.). An analysis of variance (CHAPCO and EBISUZAKI 1978) of some previously collected data involving a diallel cross among six isogenic lines (these included the four foundation stocks utilized here) revealed that for egg-to-adult survival the “maternal variance component,” although large (74%), could not account for all the observed variation. Nonmaternal effects were also significant. For this reason, it was decided that this paper would be restricted to a genetic analysis of the egg survival measurements of only the homozygous lines. Differences in egg viability could, therefore, be unequivocally ascribed to specific genotypes and, consequently, to specific segments. Genetlcs 92: 595-601 June. 1979