Scientists fix bugs in our understanding of...( What makes a human different from a ...)

What makes a human different from a chimp? Researchers from the European Molecular Biology Laboratory's European Bioinformatics Institute [EMBL-EBI] have come one important step closer to answering such evolutionary questions correctly. In the current issue of Science they uncover systematic errors in existing methods that compare genetic sequences of different species to learn about their evolutionary relationships. They present a new computational tool that avoids these errors and provides accurate insights into the evolution of DNA and protein sequences. The results challenge our understanding of how evolution happens and suggest that sequence turnover is much more common than assumed.

"Evolution is happening so slowly that we cannot study it by simply watching it. That's why we learn about the relationships between species and the course and mechanism of evolution by comparing genetic sequences," says Nick Goldman, group leader at EMBL-EBI.

The four letter code that constitutes the DNA of all living things changes over time; for example individual or several letters can be copied incorrectly [substitution], lost [deletion] or gained [insertion]. Such changes can lead to functional and structural changes in genes and proteins and ultimately to the formation of new species. Reconstructing the history of these mutation events reveals the course of evolution.

A comparison of multiple sequences starts with their alignment. Characters in different sequences that share common ancestry are matched and gains and losses of characters are marked as gaps. Since this procedure is computationally heavy, multiple alignments are often built progressively from several pairwise alignments. It is impossible, however, to judge if a length difference between two sequences is a deletion in one or an insertion in the other sequence. For correct alignment of multiple sequences, distinguishing between these two events is crucial. Existing met
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