The answers that lie in the shape of our genes

The Origins of Genome Architecture. Author Michael Lynch. Edition First. Publisher Sinauer Associates. Pages 389. Price £39.99. ISBN 9780878934843.

May 22, 2008

Thanks to relatively recent developments in technology, information on the genomes of living (and, indeed, extinct) species is accumulating at an unprecedented rate. These data show very clearly that organisms differ greatly in the size, structure and composition of their genomes. While the genomes of unicellular bacteria contain a number of genes and not much else, the genomes of complex multicellular eukaryotes are bloated by an impressive amount of non-coding DNA. Some of the non-coding material, such as introns and untranslated regions, can be considered part of genes, but a considerable portion consists of genomic parasites that make up the majority of the genomic DNA in some species.

The Origins of Genome Architecture deals with how to explain the observed diversity in genome structure. It provides a review of the current hypotheses and data, and it also integrates previous work into a rigorous population genetic framework - for a good reason. For Michael Lynch's main thesis is that previous studies were rooted in a selectionist tradition going back at least to geneticist R. A. Fisher and assume that present genomes and their structure represent an adapted state. According to Lynch, however, this might not be generally true. The central argument of his book is that populations of many multicellular organisms are of a size small enough for evolution to be largely driven by genetic drift - that is, fluctuations in gene frequencies because of chance events rather than the genetic fitness of the reproducing individuals. This random component of evolution, Lynch argues, is likely to overwhelm the subtle selection pressures acting on many of the (non-coding) genomic features, leading to the fixation of potentially suboptimal variants in these species.

After some introductory chapters, Lynch sets out his thesis by providing both the population genetic foundation and the empirical data to support it. In the remainder of the book he reviews one by one the most important genomic features, summarising existing data and hypotheses and, in most cases, providing an alternative neutralist explanation for many of the adaptive scenarios put forward by other authors.

Lynch's book is extremely valuable, for several reasons. First, he has invested great effort in providing an up-to-date and in-depth review of the literature, making his book a very useful source of information on current hypotheses and empirical data on genome evolution. Second, the book serves as a reminder to all those working in the field (especially those lacking a population genetic background) that evolution is not equivalent to natural selection. As Lynch argues, stochastic processes can have a considerable impact on the evolutionary outcome if populations are small and/or selective pressures weak. For this reason, population genetic theory should be used to establish neutral null hypotheses against which adaptive scenarios can be tested. Finally, the book illustrates - inadvertently - the importance of conducting research with an open mind, because in his arguments against the dogma of selection Lynch sometimes appears to become just as dogmatic about the importance of drift. Whether his arguments turn out to be right or not, his book will undoubtedly contribute to an increased appreciation of neutral processes in the origins of genome architecture.

  • Who is it for? Anyone interested in genome evolution, from graduate students to established researchers.
  • Presentation - Chapters are in logical order, with comprehensible figures.
  • Would you recommend it? Yes. An extremely useful book, if read critically.

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