P-Element-Induced Variation in Metabolic Regulation in Drosophila

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Movement of transposable elements has been demonstrated to be a cause of genetic variation that is relevant to quantitative characters in Drosophila. Here a particular class of P-element-induced variation known to be mediated through changes in expression of targeted enzyme-encoding genes is examined. Balancer chromosomes and the ``jumpstarter'' modified P-element were used to construct 124 second-chromosome and 139 third-chromosome lines of Drosophila melanogaster bearing unique stable P-element insertions in a common genetic background. Lines that were homozygous for second-chromosome P-element insertions were significantly more heterogeneous than control lines in 10 of 16 characters, whereas third-chromosome insertion lines were heterogeneous in 11 of the 16 traits. The average mutational variance per insertion relative to environmental variance (V(m|1)/V(e)) was 5.7 X 10(-2), and estimates varied widely across characters. The distributions of mutational effects tended to be skewed, with a longer tail toward high enzyme activities. Mutational effects deviated from a normal distribution in 15 of the 16 traits and significant outlier lines were found in both a positive and negative direction in several characters. Pleiotropic effects of single P-element insertions were quantified by correlation, and, after correcting for simultaneous tests, of the 91 correlations, 37 were significant at the 5% level. The pattern of pleiotropic effects deviated both from the equilibrium genetic correlations quantified in a previous study and from the correlations of mutational effects in a mutation-accumulation experiment, suggesting that multiple forces are at play that shape extant variation.

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