Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 24

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych:  B chromosome
help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
A change of B-chromosome frequencies in the population of Apodemus flavicollis (Melchior, 1834) from Cer mountain in Yugoslavia was studied. Five samples were collected during 1989. Specimens with Bs were present in all samples with frequencies ranging from 0.22 to 0.39. Differences between frequencies of animals with Bs in successive samples were not statistically significant. The change in the population size (n) was positively correlated with variation in frequency of animals with Bs (rp = 0.81), but negatively with frequency of Bs per B carrying animals (rp = -0.65). A analysis of variance of external body measures and some cranial characters showed no significant differences between animals with and without Bs.
Spatial and temporal distribution of supernumerary or B chromosomes were studied in natural populations of wood mice. A total of 859 individuals belonging to several species from Eurasia were examined. A very high percentage of individuals possessing B chromosomes was found in Apodemus peninsulae (97.9%, n = 47), a high percentage in A. flavicollis (42.5%, n = 362), and a low one in A. syluaticus (2.4%, n = 210). No B chromosomes were observed in A. uralensis (n = 10), A. fulvipectus {n = 19), A. hermonensis (n = 1), A. agrarius (n = 58), A. mystacinus (n = 7), and in Apodemus species collected in Turkey (n = 74), Israel (n = 1), Azerbaijan (n = 2), Tadjikistan (n = 24), and Kyrghyzstan (n = 44). A modest to high frequency of B chromosomes was thus observed particularly in the species confined to a forest environment, whereas no B's were found in the species dwelling in open, steppe-like or rocky habitats. Both in A. peninsulae and A. flavicollis the frequency of B chromosomes varied among local populations. Follow-up studies revealed stability in the respective proportions of B chromosomes during subsequent years. However, no unambiguous interrelationship could be found between the frequency of B chromosomes and various biological and/or ecological variables. Therefore it seems that the incidence of B chromosomes is mainly determined by stochastic effects operating within the specific genetic background of a population.
The presence of B chromosomes in the yellow-necked mouse Apodemus flavicollis (Melchior, 1834) was analyzed in 320 adult animals from four localities in Yugoslavia. Our aim was to assess the effects of B chromosomes on certain morphometric charac­teristics. The characters that were chosen are included in the taxonomic discrimination of this particular species as well as the sibling species Apodemus sylvaticus (Linnaeus, 1758). B chromosomes were found in all the localities with frequencies ranging from 21.6% to 42.9%. It was ascertained that different frequencies of animals with B chromo­somes change the slope of the regression curve of the length of foramina incisiva (FI) relative to the distance from the 3rd upper molar to the incisor (IM3). This finding questions the validity of use of this relative value in taxonomy without taking into consideration karyological data. It was also established that the relative length of the tail (the body/tail ratio) significantly increase in the presence of B chromosomes. As this index demonstrates significant geographic variability the result could be taken as a trend only.
In this study, somatic chromosome counts were determined in 302 individuals from 43 Allium przewalskianum populations; 90 were diploids (2n = 16, 16 + 1B, 16 + 2B) and 212 were tetraploids (2n = 32). Of the 43 populations, five were selected for karyotype analysis. Among them, the diploid plants have two karyotypes: 2n = 2x = 14m + 2st (2SAT) and 2n =2x = 8m + 6sm + 2st (2SAT). The tetraploid has one: 2n = 4x = 28m + 4st. Mixoploidy, Robertsonian translations, and B chromosomes were reported for the first time. In combination with previous chromosome data, the present study reveals a uniform basic chromosomal number (x = 8) and uniformity of karyotypes (Stebbins's 2A type), indicating that speciation through polyploidization is less likely in A. przewalskianum, despite the highly diversified habitats it occupies.
During this study, 94 specimens (51 males, 43 females) of the wood mouseApodemus sylvaticus (Linnaeus, 1758), the yellow-necked mouseA. flavicollis (Melchior, 1834) and the western broad-toothed mouseA. epimelas (Nehring, 1902) from 20 localities of Greece were karyologically examined. The first two species were found to be widely distributed and their otherwise very similar karyotype (2n=48, FN=48) could be clearly distinguished, based on C-banding pattern. The third species appeared to have a more limited geographical distribution and its karyotype was distinguished from that of the previous two species, since it contained two pairs of small metacentric autosomes (2n=48, FN=52). The chromosomal study further revealed that nine individuals ofA. flavicollis possessed supernumerary B chromosomes (2n=49–50, FN=49–50). Meiotic chromosome preparations revealed that in contrast to sex chromosomes and autosomes, B chromosomes do not participate in bivalent formation. On the other hand, no supernumerary chromosomes were found in the studiedA. sylvaticus andA. epimelas material.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.