Diversity of Short Sequences Among Genomes of Inversion Strains in Drosophila Pseudoobscura

Open Access
Author:
Lee, Megan E
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Stephen Wade Schaeffer, Thesis Supervisor
  • Richard W Ordway, Honors Advisor
Keywords:
  • Drosophila Pseudoobscura
  • Drosophila
  • inversion strains
  • short sequences
  • repeats
  • inversion
  • cline
  • polymorphic
  • motifs
Abstract:
A chromosomal inversion is a mutation that occurs when the DNA of a chromosome is broken in two places and rejoined such that the order of central genes on the chromosome is reversed. Species of Drosophila differ in levels of chromosomal inversions across the different chromosomes of their genomes. D. subobscura, a close relative of D. pseudoobscura, has chromosomal inversions on all of its chromosomes. The chromosomes of Drosophila pseudoobscura also differ in their degrees of rearrangement. The third chromosome is polymorphic for over 30 chromosomal inversions in North American populations of D. pseudoobscura, while the other four chromosomes are monomorphic for gene order. The mechanisms that lead to some chromosomes to be inverted or not is not clearly understood, but it has been observed that repeat sequences are often present in inversion breakpoints, the site of chromosomal breakage. The objective of this work is to test the hypothesis that different inverted chromosomes have similar sets of repetitive nucleotide sequences. Multiple computer programs were written and used to detect sequence differences and similarities between the genomes of inversion arrangements. The resulting data shows that there were not many major differences in repeats among the arrangements except for the sequences in Pikes Peak, which showed more divergence from the other arrangements, suggesting differences may have accumulated in that arrangement. The highly differentiating repeat sequences were enriched for G, C, and T bases.