Theses and Dissertations

Issuing Body

Mississippi State University


Counterman, Brian A.

Committee Member

Outlaw, Diana A.

Committee Member

Reed, Laura K.

Date of Degree


Document Type

Graduate Thesis - Open Access


Biological Sciences

Degree Name

Master of Science


College of Arts and Sciences


Department of Biological Sciences


Sex chromosomes and autosomes often differ in their relative rates of evolution, with sex chromosomes generally accumulating changes more rapidly (faster-X evolution). Transposable elements (TEs) make up a significant portion of eukaryotic genomes and are some of the most rapidly evolving genetic elements. We compared relative rates of insertion on the X and autosomes for 78 families found in Drosophila melanogaster. The average X/A ratio for these TE families was 1.11, similar to the mean dS X/A ratio, indicating no male-bias in mutation rate or TE insertion. The major mode of the distribution was ~0.8, indicating stronger purifying selection on the X chromosome for most TEs. We found no effect on X/A from sex-specific TE expression, but TEs with male-specific piRNA had an average X/A ratio of 0.62. We also found that TEs with very high X/A ratios (top 5%) had X chromosome insertions in areas of relative low recombination.



recombination rate||piRNA||expression||sex-bias||sex-specific||drosophila melanogaster