Embargoed until: 19:00 24 May 2000

Understanding Evolution - Advances at IFR

Scientists at the Institute of Food Research in Norwich, and the Universities of Manchester and Oxford are trying to understand how chromosomes evolve and new species arise. A paper in Nature (25 May 2000) describes our latest findings.

Dr Ian Roberts, project leader from the National Collection of Yeast Cultures at IFR, said "Understanding chromosome evolution is a basic step towards understanding the evolution of species and biodiversity in general."

We are interested in understanding how whole genomes evolve and which are the critical changes in genetic material that result in the evolution of new species. We think several types of change to DNA are involved in the formation of new species; the most important was thought to be chromosomal rearrangements - where a region of DNA swaps between the arms of a pair of chromosomes. However, in a paper to be published in Nature (25 May 2000) we show that this process alone was not responsible for producing new species of yeast.

Dr Ian Roberts, describing the work, said "We try to put yeast species on a family tree in order to have a framework for understanding their characteristics and to rapidly identify new strains as they get sent in to us from food spoilage and other sources. This gives us a way of looking at how the difference between species increases over evolutionary time and how far back we have to go to find the last common ancestor."

Yeasts are useful for studying the evolution of species, as the complete DNA sequence of baking yeast (Saccharomyces cerevisiae) has been available since 1996, and a number of closely related species have been described recently.

Techniques developed for studying the yeast genome, and differences between closely related yeast species will eventually assist scientists to understand the human genome, and how it can be compared with other completed, but not closely related, genomes (eg the mouse genome, which is also being completely sequenced at the moment).

• Reference: Fischer G, James SA, Roberts IN, Oliver SG & Louis EJ. Chromosomal Evolution in Saccharomyces. Nature 405 451-454.
• This project has been funded by the BBSRC Genes and Developmental Biology Committee.
• The mission of the Institute of Food Research is to carry out independent basic, and strategic research on food safety, quality, nutrition and health. It is a company limited by guarantee, with charitable status, grant aided by the Biotechnology and Biological Sciences Research Council (BBSRC).
• The Institute is based on the Norwich Research Park.

• There are several ways in which this could happen: chromosomal rearrangements such as translocation (swapping over) of regions between arms of a chromosome pair; simple errors in replication due to failures of mismatch repair systems and accumulation of major gene differences due to random genetic drift. The relative importance of these processes it not known, but comparing the incidence of the different types of chromosome changes in closely related species is a way of finding out.
• The yeast genus Saccharomyces is useful for studying the evolution of species, as the complete genome sequence of S. cerevisiae (baking yeast) has been available since 1996, and a number of novel, closely related species have been described recently. This group has compared the number of chromosomal rearrangements and sequence phylogeny (evolutionary relationship) between 3 new Saccharomyces species (S. cariocanus, S. mikatae, S. kudriavzevii) and 2 other closely related yeasts (S. bayanus, S. paradoxus) using S. cerevisiae as reference. Their results suggest that chromosomal rearrangements do not occur at a constant rate, contrary to previous opinion.

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