The Genetic Architecture of Drosophila Sensory Bristle Number

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Title: The Genetic Architecture of Drosophila Sensory Bristle Number
Author: Dilda, Christy Lynn
Advisors: Dr. Bruce Weir, Committee Member
Dr. Greg Gibson, Committee Member
Dr. Michael Purugganan, Committee Member
Dr. Trudy F. B. Mackay, Committee Chair
Abstract: Quantitative traits vary continuously in populations due to the segregation of multiple loci (QTL, or quantitative trait loci) and sensitivity to environmental variation. In order to describe quantitative variation in terms of complex genetics, rather than statistically, we mapped QTL on the X and third chromosomes affecting Drosophila sensory bristle number, and determined their effects and interactions in three temperature environments. Recombinant inbred (RI) mapping populations for each chromosome (C1, LST; C1, HST; C3, LST; C3, HST; C3, LAB; C3, HAB) were derived by crossing lines selected for low (L) or high (H) sternopleural (ST) or abdominal (AB) bristle number to a standard inbred strain with wild type bristle numbers (Sam). Recombination breakpoints were determined using polymorphic roo transposable element insertion sites. In order to estimate additive and dominance QTL effects, as well as QTL × environment interaction, each RI line was crossed to Sam and the other parental strain, and the progeny were raised in three temperatures: 18, 25, 28 degrees Celsius. Bristle number QTL were mapped separately for each chromosome, trait and environment by linkage to roo marker loci, using composite interval mapping. This method tested the hypothesis that an interval flanked by two adjacent markers contains a QTL affecting the trait, while controlling for the effects of segregating linked QTL on the same chromosome by multiple regression on markers outside the test interval. The significance level of the likelihood ratio (LR) test statistic was determined by permutation. The presence of a QTL was inferred if the LR test statistic exceeded the critical value, with the most likely location of the QTL the map position corresponding to the peak LR. 2LOD support intervals were given as approximate 95% confidence intervals for the location of each QTL. A total of 142 QTL were mapped for sternopleural and abdominal bristle number, pooled over all six mapping populations, three temperature environments, and two sexes. Generally the effects of the QTL were moderately large. QTL effects were often sex- and environment-specific. The significance of QTL × sex, QTL × temperature interactions and epistatic (QTL × QTL) interactions was determined by analysis of variance (ANOVA), with the significance level determined using Bonferroni correction. Interactions with sex and temperature were common for QTL affecting both sternopleural and abdominal bristle number, but were more frequent for the latter trait. QTL effects were also contingent on genetic background. There were 30 significant epistatic interactions (9.0%) affecting sternopleural bristle number and 25 significant epistatic interactions (11.0%) affecting abdominal bristle number, after Bonferroni correction. Comparisons made between the six populations showed a total of 53 individual QTL, of which 11 mapped to the X and 42 to the third chromosome. A total of 33 and 31 QTL were found to affect sternopleural and abdominal bristle number, respectively; of these 11 QTL affected both bristle traits. Many of the QTL mapped to the same location as candidate bristle development loci, but several QTL regions did not encompass obvious candidate genes.
Date: 2002-08-19
Degree: PhD
Discipline: Genetics

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