The formation of two separate species from a single ancestor, and the subsequent maintenance of these new species without hybridization, is a central problem in evolutionary biology. The availability of entire genomes in a range of organisms could help address the problem, as E. J. Louis of the University of Oxford and colleagues now explore in Nature 1 .
Chromosomes are the bodies along which genes are arranged in a linear order.
Because of chromosomal rearrangements, sperm and egg cells may have too many chromosomes, or too few. This can prevent the successful development of fertile or viable offspring. Chromosomal rearrangement, therefore, could be a useful way of enforcing the differences between two otherwise very similar species, and has indeed been observed in several cases. The researchers mapped the pattern of chromosomal rearrangement in brewers' yeast and its relatives. If chromosomal rearrangement has been a constant, consistent factor in speciation, then we would expect a greater amount of rearrangement with evolutionary time.