Mutation rate, genome size and their relation to the rec concept

Abstract

ORGANISMS vary greatly in genome size, that is, in the amount of DNA comprising the haploid genome. Rates of radiation-induced mutation expressed as mutations per locus per rad, also differ widely among organisms, but it is surprising that mutation rates and genome size are correlated¹. This correlation is unexpected because proteins are of a similar size in all organisms, implying that structural genes must also be of a similar size. Accordingly, one would expect that, although the overall mutation rate would be proportional to the overall number of genes, the mutation rate per locus would be similar in all organisms or, at least, bear no relation to genome size. Surveying published data, however, Abrahamson et al.¹ found a direct correlation between rate of radiation-induced mutation and size of the haploid genome from Escherichia coli to Hordeum vulgare (the ABCW relationship). We wondered whether rates of chemically induced mutation would also be related to genome size, both because of the practical importance of being able to extrapolate to the genetic effect of a chemical on the human population and because the information might help to elucidate the mechanism underlying the ABCW relationship.