NTU Undergraduates' research April 2014 - Biosciences | Page 9
Releasing evolutionary constraint: Functional
complementation of an alternative reading frame
Sophy H Conway
Abstract
Experimental evolution of bacteriophage provides an insight into the genetics of adaptation and
fitness. Since the sequencing of PhiX174 by Sanger and colleagues (1977), the bacteriophage has
been utilized in numerous experiments due to its small genome size and non-pathogenic properties.
This investigation aims to identify the evolutionary adaptations that occur in an ancestral strain of
PhiX74 and in an amber mutant strain whilst cultured with the amber suppressor, E.coli strain BAF8.
Utilizing two cultures, a short term and a long term culture, it was hypothesised that fitness would
increase over time. The hypothesis to be tested was that Am3 would undergo a mutation, with a
possibility of wild-type reversion, suppressing the amber mutation. An overlay assay provided
evidence for fitness adaptation. Results of DNA sequencing of phage DNA revealed no genetic
adaptation. The results regarding suppression of the amber mutation revealed suppression was
limited to the level of expression with no evidence for genomic change. This finding provided
support for the argument against Crickâs (1966) concept of a frozen genetic code, enhancing
evidence from previous research (Ibba and Soll, 2000; Santos et al, 2006; Hammerling et al, 2014).
Keywords: PhiX174, bacteriophage, amber mutant, amber suppression, evolution