Speciation, Chromosomes, and Genomes: Figure 1.

Speciation, the formation of species, is an elusive yet vitally important process for evolutionary biologists to understand. Its elusiveness stems from three factors. First, a lack of agreement as to what we mean by species, which continues to cause no end of confusion; Tremaux’s statement in 1865 that ‘‘of definitions of species there are as many as there are naturalists’’ remains largely true (Nelson 1989). Second, speciation is a difficult or near impossible process to study directly (depending on the definition of species adopted). Third, in most cases, we know very little about the genetic basis of species formation. What relevance then does such a woolly and poorly understood process have to genome biologists? My aim is to show that an appreciation of speciation is important for a full understanding of genomes. I will discuss speciation in relation to a familiar animal model: the house mouse (Western subspecies, Mus musculus domesticus), which has become a key system because of its phenomenal tendency to undergo chromosomal rearrangement in nature. The extent of this extraordinary genome repatterning was highlighted recently by Garagna et al. (1997), which is the latest in an extensive series of studies on chromosomal variation in wild house mice dating back nearly 30 years (Gropp et al. 1969).