Inference of Heterosis and Epistasis in Transposon Tagged Drosophila
- Andrew G. Clark
One of the problems associated with statistical inference of gene interactions has been the relatively low power of most methods. By constructing known genotypes and measuring the phenotypes of these genotypes, novel and powerful tests of effects of mutations on phenotypic expression can be performed. Clark and others produced and analyzed a set of 263 lines of Drosophila melanogaster that had single, random transposable P-element insertions in the genome. Activities of 12 enzymes in intermediary metabolism were quantified along with levels of stored triacylglycerol and glycogen, total protein, and live weight. The tagged lines exhibited significant heterogeneity in II of the 16 metabolic characters, and a surprising 58% of the P-element insertions affected at least one character. This result implies that these genes are regulated through a highly interactive network, such that many changes in the genome affect the expression of many genes. Simple crosses among such P-element tagged lines allow for the construction of all possible two-locus genotypes for each pair of P-elements. Analysis of phenotypes of the nine genotypes provides direct estimates of additive, dominance, and epistatic effects of the mutations. Least squares fits to linear models of Cockerham indicate that 14% of the tests exhibited significant epistatic effects, and of the significant tests, 74% are either additive × additive or dominance × dominance epistasis. In general, it appears that novel mutations have epistatic effects on metabolic traits that are on the same order of magnitude as main (additive and dominance) effects. P-element insertions whose effects were heterotic also were significantly more likely to be those that manifested dominance × dominance epistasis.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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