Abstract
The origin of species is one of the central questions in evolutionary biology. Mayr (1995) defined species as groups of interbreeding natural populations which are reproductively isolated from one another. One of the potential reproductive barriers is the chromosomal rearrangement. Species, even closely related ones or even races within species, may differ drastically in number and composition of their chromosomes. When different chromosomal variants hybridize, their hybrids may suffer a reduced fertility due to problems arising during meiosis. In addition, chromosomal rearrangements can change the linkage between genes that may can lead to reproductive isolation. In this thesis, I study the effect of Robertsonian translocations, a common chromosomal rearrangement in which two acrocentric chromosomes fuse into a metacentric, on reproductive isolation in wild western house mice Mus musculus domesticus. Hybrids between chromosomal races of house mice suffer various degrees of fertility reduction, from no reduction to complete sterility, depending on the complexity of the chromosomal differences between their parental races. The majority of research has focused on hybrids with lower complexity, however here I investigate hybrids with higher chromosomal complexity. My results show that even a very high complexity of chromosomal variation between chromosomal house mouse races does not lead to complete reproductive isolation, as female hybrids retained some fertility, albeit greatly reduced (Chapter I). The investigation of a possible effect of Rb translocations on recombination showed that they had the potential to reduce gene flow, even though no significant effect on recombination frequency was found. (Chapter II). Genetic analysis of wild chromosomal races confirmed that differences in Rb translocations between chromosomal races influenced genetic differentiation, with increased linkage and differentiation near centromeres of Rb translocation not shared between races (Chapter III). All results together show that fertility decrease and the accumulation of different Rb translocations have the potential to change genetic linkage and provide regions of increased genetic differentiation, and thus may ultimately play a role in the reproductive isolation of chromosomal races.
Grize, Sofia A