MOLECULAR EVOLUTIONARY GENETICS OF INVERSION BREAKPOINT REGIONS IN DROSOPHILA PSEUDOOBSCURA
Open Access
- Author:
- Wallace, Andre George
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 29, 2010
- Committee Members:
- Stephen Wade Schaeffer, Dissertation Advisor/Co-Advisor
Stephen Wade Schaeffer, Committee Member
Hong Ma, Committee Chair/Co-Chair
Mary Poss, Committee Member
Avery August, Committee Member - Keywords:
- Chromosomal inversion
breakpoints
gene conversion
Drosophila pseudoobscura
Population Genetics
Recombination - Abstract:
- Chromosomal inversions are present on the chromosomes of many organisms. The effects of inversions on most of these organisms are frequently and extensively studied. Drosophila pseudoobscura is known to have more than 30 different inversions on its third chromosome and is one of the most frequently studied inversion systems. We employed this inversion system to study the evolutionary history of the gene arrangements that resulted from some of these inversions. The standard and most widely accepted phylogeny of the D. pseudoobscura gene arrangements was generated in the early 1900’s and the phylogeny was established using cytological analyses. The fairly recent sequencing of the D. pseudoobscura genome enabled us to develop a large molecular dataset to investigate the phylogeny of the inversion system. The dataset contained regions near inversion breakpoints because these regions are potentially informative because recombination is suppressed at inversion breakpoints. Several non-breakpoint regions were also included in the data set. There were three key questions addressed in this study. 1) Is the origin of the inversion polymorphism monophyletic? 2) Is the molecular phylogeny consistent with the cytological phylogeny? 3) Which arrangement is the ancestral in the D. pseudoobscura population? We were able to provide support for a monophyletic origin of this inversion polymorphism and our results also provided support for the cytological phylogeny. Though further experimentation is necessary to identify the exact ancestor, we were able to determine that the ancestral arrangement is either the Santa Cruz or the Hypothetical arrangement. A population genetics study was also performed using the same dataset. In this study, we investigated how nucleotide diversity within and between D. pseudoobscura inversions was altered by differences in the levels of genetic exchange across the chromosome. Consistent with theoretical predictions, regions within the proximal segment had lower levels of recombination than regions in the distal segment of the chromosome. We also identified one inversion (PP) that shared more genetic information with all other arrangements than any other arrangement studied. Finally, our results indicated that positive selection is acting on this species and that this species has recently experienced a population expansion.