CONICET | Buscador de Institutos y Recursos Humanos

Genetically distinct forms within species may generically be called 'races'. The areas where such races meet and interbreed to produce hybrid offspring are known as hybrid zones (Barton and Hewitt, 1985; Harrison, 1990). In the western subspecies of the house mouse (Mus musculus domesticus) there are many geographically local races that differ by chromosomal rearrangements from the widespread ancestral chromosomal form (Piálek et al., 2005). Therefore, chromosomal hybrid zones in this species are the geographical locations where two or more of these chromosomal races make contact and interbreed, and/or where such races interact with the ancestral chromosomal form. Hybrid zones between races differing by chromosomal rearrangements are expected to be 'tension zones', i.e. areas maintained by hybrid unfitness, with well-defined properties including a tendency to minimize their length (Barton and Hewitt, 1985). Pairing and segregation abnormalities associated with heterozygous meiotic configurations in hybrid offspring often lead to reduced fertility in chromosomal hybrid zones, including those of the house mouse (Searle, 1993). However, as we will show in this chapter, there is far more to the chromosomal hybrid zones of the house mouse than their simple description as 'typical' tension zones. We discuss past and future work to develop house mouse chromosomal hybrid zones as models to study the role of chromosomal rearrangements in genetic subdivision, race-formation, and speciation, and to understand chromosomal hybrid zones in the context of chromosomal evolution. Before considering what has been discovered in chromosomal hybrid zones, we will present relevant background on the nature of the chromosomal variation in the house mouse and on the chromosome heterozygosity that defines F1 and other hybrids formed at the meeting of chromosomal race.

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