Abstract
Arguably, the three central pillars mitochondrial DNA (mtDNA) evolution that make it a powerful tool for evolutionary studies are maternal inheritance, lack of
recombination and high copy number. While it is likely that these three pillars cooccur
in most higher eukaryotes it is important to consider mechanisms causing these
mainstays to fail. One such mechanism causing failure of strict maternal inheritance is
paternal leakage. The occurrence of paternal leakage followed by its transmission to
offspring may bias the interpretation of mtDNA as a molecular marker by introducing
additional haplotypes into the mtDNA pool of a single population and create
individuals with more than one type of mtDNA (heteroplasmy). The presence of
paternal mtDNA can potentially affect a variety of disciplines including evolutionary
genetics, molecular ecology, biogeography, mitochondrial medicine, and forensic
science. Here, I examined the frequency of paternal mtDNA transmission in
intraspecific crosses of Drosophila simulans harbouring distinct mtDNA haplotypes.
First I optimized two primer sets. In initial optimization studies I could detect as little
as 0.1% paternal mtDNA in an individual. Second I assayed a total of 33 individuals
from each of the 62 intraspecific crosses. Two crosses and six individuals present
strong evidence for mtDNA paternal leakage indicating the paternal leakage was in
the order of 0.3%. The main limitations of this study were the detection levels of the
specific primers and the need to complete the reciprocal cross to corroborate the
results presented. This experiment clearly showed the notable contribution of paternal
mtDNA leakage to the inheritance of mitochondria. Further study regarding
estimation of sperm/oocyte content and the mechanisms leading to elimination of
paternal mtDNA such as ubiquitination of sperm mitochondria in different species
may lead to better understanding of this mechanism.