A new look into the genomes of natural populations of the common house mice by a team of researchers suggests that large-scale chromosomal rearrangements play an important role in speciation.
Alterations to chromosomes are considered important in speciation (the process by which new species are formed). This is because several chromosomal rearrangements can make the genome of a few individuals in a population so different that they cannot successfully interbreed with the rest of the population. It is believed that, over time, this can lead to the evolution of two distinct species with different karyotypes (i.e. different sets of chromosomes making up the genome). In-depth testing of these ideas is now possible with advanced molecular technologies, which allow researchers to sequence DNA across entire genomes.
In a new paper in the journal Molecular Biology and Evolution, researchers from the University of Konstanz, Harvard University and La Sapienza University of Rome, study wild house mice (Mus musculus domesticus) from several islands in the Aeolian archipelago off the coast of Sicily, Southern Italy. Their findings provide empirical support to the idea that a specific type of large-scale chromosomal rearrangements called «Robertsonian (Rb) fusions» play an active role in speciation.
Elucidating the role of chromosomal rearrangements in speciation
Chromosomal rearrangements are mutations within the genome of an individual, a population or an entire species where large pieces of the genome change, for instance through duplication (where an entire chunk of a chromosome is duplicated) or inversion (where a part of a chromosome changes its orientation relative to the rest of the chromosome). «The most common type of chromosomal rearrangement to occur in the natural house mouse populations of Western Europe are Robertsonian fusions,» explains Dr Paolo Franchini, first author on the study and a researcher in the University of Konstanz?s zoology and evolutionary biology research group led by Professor Axel Meyer.
Robertsonian fusions are large-scale chromosomal rearrangements where two entire chromosomes fuse to form one very large metacentric (X-shaped) chromosome. «This type of rearrangement is known to play a considerable role in speciation,» says Franchini. «And it happens to be very common in wild house mice, which makes them a perfect study system. The added advantage with the Aeolian mice is that these populations are very small and genetic mutations are likely to spread rapidly through the population of a given island.»
The wild house mouse populations in the Aeolian archipelago, which consists of seven small islands of volcanic origin, have different karyotypes characterized by different combinations of Robertsonian fusions. One of the main goals in studying these populations was to understand how these karyotypic distributions evolved — that is, to reconstruct their evolutionary history.
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