Jumping around the Topic of Mobile Genetic Elements

he uses as a case of " major genome restructuring " (p. 11) of Mobile Genetic Elements is that of P elements in Drosophila whose mobilization cause a syndrome of genetic traits called hybrid dysgen-esis. P elements invaded the genome of D. melanogaster Mobile Genetic Elements in historically recent times, but, as Shapiro fails to note, Edited by David J. Sherratt they did not invade the genome of D. simulans, a closely New York: IRL Press at Oxford University Press. (1995). related species. Yet, the genomic organization of these 179 pp. $105.00, hardcover; $52.00, paperback. two species remains almost identical. Shapiro's major restructuring is nowhere to be seen. Instead of a Fluid Genome, it is more useful to think of mobile DNA as a small but turbulent component of fluidity within a still Genetic information is often compared to the text in a mostly constant genome. book or to a computer program, but these well-worn Another of Shapiro's themes is that of the " biological analogies break down when we consider mobile DNA. utility " (p. 8) of transposable elements to their host or-Books don't rewrite themselves while you are trying to ganisms. Transposable elements, in other words, are read them, and computer programs don't rearrange their good for you. This view stands in sharp contrast to code during execution, at least not intentionally. Mobile another chapter in the book by John Brookfield who DNA exists in virtually all organisms, and it is essential makes the case for transposable elements as genomic to many. It ranges from single-purpose mechanisms parasites. Both authors mention antibiotic resistance such as mating type switching in yeast to the near ubiq-factors carried by bacterial transposons as an example uity of transposable elements, many of which function of how selection could favor mobile elements. For Sha-equally well in a wide variety of species. While transpos-piro this situation represents the rule, whereas, for able elements are often considered to be molecular par-Brookfield, it is the exception (unfortunately, neither au-asites, other forms of mobile DNA, such as those which thor mentions the only other clear case of biological produce antigenic variation, have clear beneficial func-utility of transposable elements, namely the telomere-tions for the organism. forming retrotransposons in Drosophila). Unlike Shapiro, Mobile Genetic Elements is a new book on the subject Brookfield places his arguments in the framework of edited by D. Sherratt. If the topic itself is diverse …