Biology Ph.D. Dissertations

Title

Effects of Non-Standard Alternative De Novo Mutations on Evolution of Drosophila Melanogaster

Date of Award

2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Biological Sciences

First Advisor

Ronny C. Woodruff (Advisor)

Second Advisor

Joshua B. Grubbs (Other)

Third Advisor

Maria Bidart (Committee Member)

Fourth Advisor

Paul F. Morris (Committee Member)

Fifth Advisor

Scott O. Rogers (Committee Member)

Abstract

Most mutations that occur within the autosomes of eukaryotic multicellular organisms are known to be mildly deleterious in effect, and are masked from selective pressures governing removal and fixation by their occurrence in the heterozygous state. Genetic drift, selection, and dominance all play a role in determining whether a mutation will be fixed or removed from a population, and affect the ultimate fitness of the organism possessing the new mutational variant. This understanding, however, applies primarily to mutational events occurring in autosomes during the adult phase of the organism’s life cycle. The effect of a de novo mutations on organismal fitness can differ greatly however, depending upon when in the life cycle and the ploidy of the chromosome these mutations arise in. Mutations arising in the gender with a haploid sex chromosome are immediately expressed and exposed to selective pressures in the hemizygous state, whereas mutations arising in the gender possessing diploid sex chromosomes are concealed from expression and selective forces in the heterozygous state. Due to this heterozygous condition the diploid sex-chromosomes may accumulate a large number of mildly deleterious mutations over an organisms’ life span, resulting in gender-based differences in fitness due to differences in expression and the number of mutations accumulated. Our expectations of how de novo mutations may affect organismal fitness can also be subverted by the effects of a single mutation arising in primordial germ cells (PGC) before they undergo sequestration. PGC’s sequester and suspend almost all genetic processes for a period of time before migrating to their future site of development, and it is believed that part of the reason for this sequestration is to prevent single de novo mutations from developing into cluster mutations. In order to understand how new mutations affect population fitness in a variety of changing environmental conditions, a greater understanding of conditions that can modify how new mutations affect population fitness is needed. This work attempts to identify some of these conditions, and to detail how mutations arising in these conditions affect fitness of a population across generations.

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