Microsatellites mapping for non-model species with chromosomal rearrangement: a case study in the frog Quasipaa boulengeri (Anura: Dicroglossidae)

Gene mapping is an important resource for understanding the evolution of genes and cytogenetics. Model species with a known genetic map or genome sequence allow for the selection of genetic markers on a desired chromosome, while it is hard to locate these markers on chromosomes of non-model species without such references. A frog species, Quasipaa boulengeri, shows chromosomal rearrangement polymorphisms, making itself a fascinating model for chromosomal speciation mediated by suppressed recombination. However, no markers have been located on its rearranged chromosomes. We present a complete protocol to map microsatellites based on mechanical microdissection and chromosome amplification techniques. Following this protocol, we mapped 71 microsatellites of Q. boulengeri at the chromosome level. In total, eight loci were assigned to rearranged chromosomes, and the other 63 loci might attach to other chromosomes. These microsatellites could be used to compare the gene flow and verify the chromosomal suppressed recombination hypothesis in Q. boulengeri. This integrated protocol could be effectively used to map genes to chromosomes for non-model species.

Gene flow despite complex Robertsonian fusions among rock-wallaby ( Petrogale ) species

Complex Robertsonian rearrangements, with shared arms in different fusions, are expected to prevent gene flow between hybrids through missegregation during meiosis. Here, we estimate gene flow between recently diverged and chromosomally diverse rock-wallabies ( Petrogale ) to test for this form of chromosomal speciation. Contrary to expectations, we observe relatively high admixture among species with complex fusions. Our results reinforce the need to consider alternative roles of chromosome change, together with genic divergence, in driving speciation.

Robertsonian translocation in the house mouse: a tale of chromosomal speciation

The subspecies Mus musculus domesticus has a very high chromosome number variability for the presence, in different populations, of different numbers of metacentric chromosomes. These metacentrics are derived by Robertsonian fusion, i.e. the joining of two acro/telocentrics at the centromeres. Since the discovery in 1969 by Alfred Gropp of the first chromosomal variant in an isolated mouse population of the Swiss Poschiavo Valley, more than 100 geographically distinct chromosomal races with metacentrics fixed in homozygosity have been described. The friendship and the common scientific interests among Alfred Gropp, Ernesto Capanna and Maria Gabriella Manfredi Romanini have primed a wealth of studies on the “Robertsonian phenomenon” in this species. These studies have contributed to elucidate i) the molecular bases of metacentric chromosomes formation, ii) the establishment of metacentric races and iii) the impact that chromosome heterozygosities exert on reproductive isolation and speciation.