Biology Ph.D. Dissertations


The Role of New Mutations in Evolution and Cloning: Genetic Analysis to Identify the Role of New Beneficial Mutations in Increasing Viability and Salt Tolerance in Drosophila Melanogaster and the Influence of Deleterious Mutations on Cloning Efficiency

Date of Award


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Biological Sciences

First Advisor

Ron Woodruff


Mutation and selection are major driving forces of evolution. However, the role of new beneficial mutation is considered negligible in almost all evolutionary processes. In most cases it is difficult to separate the effect of pre-existing genetic variation at low frequencies from new mutations. In this study, experiments with Drosophila melanogaster were conducted to study the effect of new beneficial mutations on increases in viability and in adaptation to increased toxic levels of dietary salt. Completely homozygous stocks were used in the experiments to eliminate the effect of pre-existing genetic variation. In the viability experiment, a modification of Dobzhansky and Spassy assay (1947) was used to demonstrate that new beneficial mutations can quickly increase viability in Drosophila populations of different sizes. By use of inbred homozygous stock it was demonstrated that adaptation of Drosophila to increased salt tolerance due to new beneficial mutations can also occur quickly. We have also documented that the accumulation of deleterious mutations can reduce cloning efficiency in somatic cells. Overall, the results of these studies support the view that new mutations along with selection can have a major influence on cloning and the evolution of organisms.