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One target system to diagnose the effects of contaminant exposure on organisms in the environment is to monitor biological damage by examining effects on their DNA.
Contaminant-induced damage results in breaks in the DNA structure. Such breaks could give rise to heritable changes and thus, population level effects, notably reproductive success (i.e. fertility and fecundity).
The Comet assay is a simple method to measure DNA damage. The principle of the technique is to induce relaxation of the negatively-charged DNA supercoils where breaks are apparent. The higher the amount of DNA breaks leads to the greater distance of migration within the gel using electrophoresis.
The relative amount of DNA migrated provides a simple method to measure the DNA breaks in an individual cell. The aptly-named Comet assay is due to the appearance of ‘comet heads’ containing the high molecular weight DNA and the ‘comet tail’ containing the leading end of molecular fragments.
The Comet Assay has been used to identify DNA damage in a number of invertebrate taxa in recent years, including three bivalve species: the common cockle, Cerastoderma edule; the blue mussel, Mytlius edulis and larvae of the pacific oyster, Crassostrea gigas during two case studies in the Tamar Estuary. Work is now continuing to examine DNA damage in a number of other candidate organisms in freshwater and coastal ecosystems.
To find out more email: A.Jha@plymouth.ac.uk