Mitochondrial Mutation: A Possible Change in the Genetic Code of Endangered Gambusia gaigei (Poeciliidae)

Seabury, Christopher

Nucleotide sequences for Gambusia gaigei consisting of a large segment of the mitochondrial cytochrome b gene were generated via the polymerase chain reaction. Four Gambusia gaigei, individuals 1, 2, 6, and 8, were chosen for further analysis simply because the cytochrome b gene sequences derived from them was of the highest quality. Three nucleotide base deletions were found to occur within the first 73 bases of the Gambusia gaigei cytochrome b gene sequence. The most notable deletion, present in all four Gambusia gaigei individuals, occurs within the first 50 bases of the cytochrome b gene sequence and rresults in the presence of two continguous stop codons. Confirmation of the stop codons has been achieved in three of the four Gambusia gaigei individuals via reverse primers. Other nucleotide base deletions as well as single stop codons appear elsewhere within the cytochrome b gene of Gambusia gaigei. Frameshift mutations, deletions of a single nucleotide base resulting in a shifted translational reading frame, occur throughout the cytochrome b gene of Gambusia gaigei. Despite the many stop codons that are produced by deleted mucleotide bases, compensatory mutations that realign the translational reading frame of the cytochrome b gene exist. Due to the presence of compensatory mutations it is hypothesized that mutant tRNA suppressors and/or tRNA wobbling may contribute to the viability of the cytochrome b gene in Gambusia gaigei.