B chromosomes of Korean field mouse &lt;i&gt;Apodemus peninsulae&lt;/i&gt; (Rodentia, Murinae) analysed by microdissection and FISH

The presence of B chromosomes was reported in six species of the genus Apodemus (A. peninsulae, A. agrarius, A. sylvaticus, A. flavicollis, A. mystacinus, A. argenteus). High frequencies of Bs were recorded particularly in A. peninsulae and A. flavicollis. The origin of Bs in Apodemus seems to be rather ancient, and it is possible that the supernumerary elements, and/or a tendency for their appearance, were inherited from the common ancestor of the extant species. We have not found any correlated changes between frequencies of Bs and the level of protein polymorphism and/or heterozygosity assessed in electrophoretic studies. No measurable effect of Bs on overall genetic variability was thus revealed in studied populations. The pattern of evolutionary dynamics of Bs can be distinctly different between geographical populations, and both the parasitic and the heterotic models can be applied to explain the maintenance of Bs in different populations. Further studies are desirable to improve our understanding of the complicated evolutionary dynamics of Bs in the Apodemus species. An essential condition for success in this respect is much more detailed information on inheritance and the molecular structure of Bs.

Section: Resultsmentioning

confidence: 99%

The mammalian model for population studies of B chromosomes: the wood mouse <i>(Apodemus)</i>

Wójcik

Macholán

et al. 2004

“…Karamysheva et al (2002), for instance, performing microdissection followed by DOP-PCR and painting metaphases with the generated probes from B chromosomes in the Korean field mouse Apodemus peninsulae, found that all B chromosomes contained a large amount of repeated DNA sequences equivalent to the pericentromeric regions of all autosomes and non-centromeric C-blocks of the sex chromosomes.…”

Section: Considerations On B Chromosomes Of Brazilian Rodentsmentioning

confidence: 99%

B chromosomes in Brazilian rodents

Silva¹,

Yonenaga‐Yassuda²

2004

B chromosomes are now known in eight Brazilian rodent species: Akodon montensis, Holochilus brasiliensis, Nectomys rattus, N. squamipes, Oligoryzomys flavescens, Oryzomys angouya, Proechimys sp. 2 and Trinomys iheringi. Typically these chromosomes are heterogeneous relative to size, morphology, banding patterns, presence/absence of NORs, and presence/absence of interstitial telomeric signals after FISH. In most cases, Bs are heterochromatic and late replicating. Active NORs were detected in two species: Akodon montensis and Oryzomys angouya. As a rule, Bs behave as uni or bivalents in meiosis, there is no pairing between Bs and autosomes or sex chromosomes and also their synaptonemal complexes are isopycnotic with those in A chromosomes.

“…They claimed that the large B chromosome arose from centric fusion as a leftover of the centromere, whereas the small B could have originated from an amplified region of an A chromosome or as an intact fragment. Karamysheva et al (2002) propose two-step appearance of Bs in A. peninsulae. Destabilization of pericentromeric regions produced by invasion of DNA sequences from euchromatic parts of A chromosomes leads to formation of microchromosomes in high frequency, which could be considered as protoBs.…”

Section: Origin Of Bs In Mammalsmentioning

confidence: 91%

“…Most Bs had one of them but some were composed of both. Karamysheva et al (2002) using whole and partial chromosome probes obtained by microdissection and DOP-PCR found that all B chromosomes in A. peninsulae contained a large amount of repeated DNA sequences which are present in many copies in pericentromeric C-blocks of all autosomes and in non-centromeric blocks of sex chromosomes. In the same species Rubtsov et al (this issue) found that DNA composition of micro and macro B chromosomes was different.…”

Section: Structure and Composition Of B Chromosomesmentioning

confidence: 99%

B chromosomes in populations of mammals

Vujošević¹,

Blagojević²

2004

B chromosomes (Bs) have been found in 55 out of 4629 living species of mammals. The summarized data show great variability in types of mammalian Bs, including differences in size, shape and molecular composition. This variability extends to the origin, mode of transmission and population dynamics. In general, B chromosomes in mammals do not differ from Bs found in other animal or plant species, but some peculiarities do exist. Most species in which Bs are found are widespread. Some data support the view that Bs may contribute to the successful expansion of some of these species, but it is possible that Bs are just more easily scored in them due to their frequent occurrence. Most of these species are also characterized by cycling fluctuations of abundance and characteristic social organization that produce conditions favorable for Bs to spread. All areas of research on Bs in mammals suffer from lack of data, emphasizing the necessity for intensified research on the molecular structure and ways of maintenance of Bs in populations.