The molecular analysis of brown eye color mutations isolated from geographically discrete populations of Drosophila melanogaster

Whole-genome effects of ethyl methanesulfonate-induced mutation on nine quantitative traits in outbred Drosophila melanogaster

We induced mutations in Drosophila melanogaster males by treating them with 21.2 mm ethyl methanesulfonate (EMS). Nine quantitative traits (developmental time, viability, fecundity, longevity, metabolic rate, motility, body weight, and abdominal and sternopleural bristle numbers) were measured in outbred heterozygous F3 (viability) or F2 (all other traits) offspring from the treated males. The mean values of the first four traits, which are all directly related to the life history, were substantially affected by EMS mutagenesis: the developmental time increased while viability, fecundity, and longevity declined. In contrast, the mean values of the other five traits were not significantly affected. Rates of recessive X-linked lethals and of recessive mutations at several loci affecting eye color imply that our EMS treatment was equivalent to approximately 100 generations of spontaneous mutation. If so, our data imply that one generation of spontaneous mutation increases the developmental time by 0.09% at 20 degrees and by 0.04% at 25 degrees, and reduces viability under harsh conditions, fecundity, and longevity by 1.35, 0.21, and 0.08%, respectively. Comparison of flies with none, one, and two grandfathers (or greatgrandfathers, in the case of viability) treated with EMS did not reveal any significant epistasis among the induced mutations.

Molecular nature of 11 spontaneous de novo mutations in Drosophila melanogaster

To investigate the molecular nature and rate of spontaneous mutation in Drosophila melanogaster, we screened 887,000 individuals for de novo recessive loss-of-function mutations at eight loci that affect eye color. In total, 28 mutants were found in 16 independent events (13 singletons and three clusters). The molecular nature of the 13 events was analyzed. Coding exons of the locus were affected by insertions or deletions >100 nucleotides long (6 events), short frameshift insertions or deletions (4 events), and replacement nucleotide substitutions (1 event). In the case of 2 mutant alleles, coding regions were not affected. Because approximately 70% of spontaneous de novo loss-of-function mutations in Homo sapiens are due to nucleotide substitutions within coding regions, insertions and deletions appear to play a much larger role in spontaneous mutation in D. melanogaster than in H. sapiens. If so, the per nucleotide mutation rate in D. melanogaster may be lower than in H. sapiens, even if their per locus mutation rates are similar.

Molecular characterization of spontaneous mutations at the scarlet locus of Drosophila melanogaster

Six spontaneous mutations of the scarlet (st) locus of Drosophila melanogaster have been studied at the molecular level. Two of the mutants (st1 and stsp) arose in laboratory populations, while the other four (stcob, stct89, stdct and stdv) were isolated from natural populations. In five of these there is a DNA insertion within the st region and in four cases the insertion has been identified as being a transposable element; these include the retrotransposons 412 and B104/roo, and also jockey a member of the LINE family. In the other case (stdct), the insertion appears to consist of partially duplicated st sequences. In two of the mutants (st1 and stdv) the same transposable element (412) has inserted in the same orientation at exactly the same site within the st gene. The transposable element insertions are found in intron and exon regions of the st gene and also in the putative upstream regulatory region; insertions located in introns or exons result in the production of truncated st transcripts. The results show that the same types of transposable elements that cause spontaneous mutation in laboratory stocks of D. melanogaster also cause mutation in the wild.