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At least 649 records · Page 36Linked to original sources
PubMed1980

Do the chromosomes of the kiwi provide evidence for a monophyletic origin of the ratites?

The extensive literature on the origin of the ratites focuses mainly on three questions: are the ratites mono- or polyphyletic, did they evolve from flying ancestors, and are they primitive or advanced? Opinion tends to accept a common descent from flying ancestors for the large ratites (for a summary of ideas see ref. 1). They would have evolved on Gondwanaland some time in the Cretaceous and have become dispersed over the southern continents after its fragmentation. However, the position of the small New Zealand kiwis, in many respects the most pecular of all birds, is still a matter for conjecture. The chromosome complements of the large ratites have been found to be remarkably uniform. The chromosome set of the kiwi, described here, clearly links up with these, which may be recorded as another indication for monophyly of all ratites. It also indicates that we are dealing here with very ancient karyotypes.

Animals↗
PubMed2002

Molecular evaluation of phylogenetic significances in the highly divergent karyotypes of the genus Gonocephalus (Reptilia: Agamidae) from tropical Asia.

The Oriental large-bodied crested dragons of the genus Gonocephalus are known to include two distinct karyomorphs. To evaluate their phylogenetic significances, we conducted phylogenetic analyses of the genus together with other agamid genera on the basis of 862 base positions of mitochondrial 12S and 16S rRNA genes. Results suggested the presence of two distinct lineages within Gonocephalus, of which one, represented by G. robinsonii that has a 2n = 32 karyotype, was closer to other Oriental agamid genera than to the other congeneric lineage. Monophyly of the latter, characterized by unique chromosomal arrangement among agamid genera (2n = 42 karyotype), was confirmed. It is thus likely that states of morphological characters shared between the two lineages are derived through convergence, or represent symplesiomorphy. Our results also suggest that the karyological similarity between G. robinsonii and several Australian agamids, pointed out in a previous study, is actually attributable to homoplasy rather than their recent common ancestry.

Animals↗
PubMed1992

A chromosomal survey of four species of gekkonid lizards.

The karyotypes of the gekkonids were serially graded from the largest to the smallest in the diploid complement. The majority of the chromosomes were subtelocentric. The diploid number was 2n = 38 in Gekko gecko and 2n = 40 in the three species of the genus Hemidactylus examined. A comparative morphometric analysis of the diploid sets of these four members suggested a cytotaxonomic relationship and a possible mode of speciation in this group of reptiles.

Animals↗
PubMed1991

Karyotype differentiation among members of the immigrans species group of Drosophila.

Karyotypes of ten species belonging to four of the five subgroups of the immigrans species group of Drosophila were examined. The group includes species with the most primitive form of karyotype as well as species with so-called recent karyotypic configurations. It is an assemblage of species with karyotypes representing five of the six successive stages involved in the evolution from 2n = 12 to 2n = 6. Implications of these findings are discussed.

Animals↗
PubMed1991

Chromosome studies on Dasypus, Euphractus and Cabassous genera (Edentata: Dasypodidae).

The somatic and meiotic chromosomes of twenty specimens of the Dasypodidae were studied. The wild specimens belonged to the genera Cabassous, Euphractus and Dasypus. The karyotype of D. novemcinctus showed a diploid chromosome number of 64, although some variation was observed in one specimen where 2n was 65, due to a supernumerary chromosome, and another had a dimorphic pair. D. septemcinctus also had a diploid chromosome number of 64, and showed two variant types due to pericentric inversions and/or centric fusions. E. sexcinctus and C. unicinctus had diploid chromosome numbers of 58 and 50, respectively. These species did not show variant chromosome types, and this was confirmed in meiotic studies. Analysis of the meiotic epithelium of species of Dasypus including the analysis of the synaptonemal complex in pachytene nuclei, showed similar findings to those commonly reported in mammalian meiosis, especially in relation to pairing and formation of the sex bivalent. The evolutionary implications of the chromosome changes in relation to organic evolution are discussed.

Animals↗
PubMed1982

Karyotypic findings in a colonic villous adenoma.

Chromosomes from a patient with a villous adenoma of the colon were examined in detail with fluorescent banding. Of the cells analyzed, 73% had a modal chromosomal number of 48-52. The karyotypic findings show clonal evolution, an additional chromosome #8 being the most frequent abnormality, suggesting that this may be the primary chromosomal change, but other changes such as loss of a Y chromosome and the presence of marker chromosome #1 with duplication of the long arm also were observed. Previous cytogenetic data on large-bowel tumors is summarized. We hypothesize that this chromosomal evidence suggests that tubular adenoma, villous adenoma, and adenocarcinoma may be interrelated steps of a growth disorder.

Adenoma↗
PubMed2003

Taxonomic status and origin of the shrews (Soricidae) from the Canary islands inferred from a mtDNA comparison with the European Crocidura species.

European island shrews are either relicts of the endemic Pleistocene fauna, e.g.,. Crocidura zimmermanni, or were introduced from continental source populations. In order to clarify the taxonomic status and the origin of the two shrew species from the Canary islands, a 981bp fragment of cytochrome b gene was investigated in all European Crocidura species and compared with the Canary shrew (Crocidura canariensis) and the Osorio shrew (Crocidura osorio). The first shares its karyotype with the Sicilian shrew Crocidura sicula (2N=36), the second with the Greater white-toothed shrew Crocidura russula (2N=42), suggesting possible sister species relationships. Results confirm the monophyly of taxa sharing the same karyotype. Genetic distances between C. sicula and C. canariensis suggest a separation since 5 Myr. The first was probably isolated from the North African ancestor after the Messinian desiccation; the second arrived on the Canary islands by natural jump dispersal. Within the 2N=42 cluster, a first split separated an Eastern line (Tunisia) from a western line (Morocco/Europe) of C. russula. C. osorio clusters together with C. russula from Spain, indicating conspecificy. This suggests a recent introduction from Spain by human.

Animals↗
PubMed1980

Tandem fusion, centric fusion, and chromosomal evolution in the cotton rats, genus Sigmodon.

G-banded and C-banded karyotypes of three closely related and morphologically similar species of cotton rats, Sigmodon hispidus (2n=52; 52 autosomal arms), S. mascotensis (2n=28; 28 autosomal arms), and S. arizonae (2n=22,24; 38 autosomal arms) are presented and compared. Despite the enormous difference between the higher diploid number of hispidus and the lower diploid numbers of mascotensis and arizonae, a great deal of G-band homology is retained. If the karyotype of hispidus is considered ancestral in the group, then chromosome evolution toward lower diploid numbers has proceeded through the fixation of a large number of both tandem and centric fusions. Centromeric heterochromatin has not, however, persisted as intetstitial C-band material on the tandem fusion products. The karyotypes of mascotensis and arizonae share several tandem fusion products of hispidus chromosomes indicating a common origin of the former two species from an ancestor of intermediate diploid number. Chromosome evolution from the ancestral hispidus-like karyotype to the karyotype of the common ancestor of arizonae and mascotensis proceeded almost exclusively by tandem fusion. This orthokaryotypic trend continued in the evolution of the karyotype of modern mascotensis. In the line leading from the arizonae-mascotensis ancestor to modern arizonae a trend of centric fusion predominated.

Animals↗
PubMed2000

An in vivo and in vitro comparison of the effects of b2-a2 and b3-a2 p210BCR-ABL splice variants on murine 32D cells.

The Philadelphia (Ph) chromosome, a characteristic cytogenetic marker of chronic myeloid leukaemia (CML), is caused by a reciprocal translocation juxtaposing the 3' region of the ABL gene onto the 5' region of the BCR gene. Due to conservation of the reading frame, but depending on the site of the breakpoint in the BCR gene, two alternatively spliced variants of the p210BCR-ABL mRNA (known as b2-a2 and b3-a2) are produced. To investigate whether there are any biological differences between these splice variants we have transfected the b3-a2 or b2-a2 cDNA into a murine myeloid cell line, 32D. We have also included the previously prepared 32Dp210 cell line (which expresses the b3-a2 transcript) in all of our comparisons. RT-PCR analysis indicated that transcription levels were comparable between the variants. Morphological examination of the cells expressing either of the BCR-ABL transcripts indicated that these cells were more mature with increased cytoplasm:nuclear ratios compared to the 32D parental and 32Dneo vector control cells. However, the 32Dp210 cells had a very different appearance from the other panel members and flow karyotyping indicated a clonal evolution and cytogenetic instability in these cells alone. At 10(6) and 10(7) cell doses all 32D cells expressing BCR-ABL caused ill health and tissue infiltration in SCID mice with such rapidity that statistical analysis was not informative. However, at the 10(5) and 10(4) dosage levels there were similar survival rates between mice injected with 32Db2-a2 or 32Db3-a2 while mice injected with 32Dp210 had a significantly shorter survival time. The study of this 32D cell line panel indicated that there were no overt differences in the biological properties conferred by the b3-a2 or b2-a2 transcripts to the 32D cells although these transcripts were able to confer in vitro and in vivo biological effects. This panel of BCR-ABL expressing 32D cells provides a useful model for CML disease progression studies.

Alternative Splicing↗
PubMed2002

Chromosomal homologies between Cebus and Ateles (primates) based on ZOO-FISH and G-banding comparisons.

ZOO-FISH (Fluorescent "in vitro" hybridization) was used to establish the chromosomal homology between humans (HSA) and Cebus nigrivitatus (CNI) and Ateles belzebuth hybridus (ABH). These two species belong to different New World monkey families (Cebidae and Atelidae, respectively) which differ greatly in chromosome number and in chromosome morphology. The molecular results were followed by a detailed banding analysis. The ancestral karyotype of Cebus was then determined by a comparison of in situ hybridization results, as well as chromosomal morphology and banding in other Platyrrhini species. The karyotypes of the four species belonging to the genus Cebus differ from each other by three inversions and one fusion as well as in the location and amounts of heterochromatin. Results obtained by ZOO-FISH in ABH are in general agreement with previous gene-mapping and in situ hybridization data in Ateles, which show that spider monkeys have highly derived genomes. The chromosomal rearrangements detected between HSA and ABH on a band-to-band basis were 27 fusions/fissions, 12 centromeric shifts, and six pericentric inversions. The ancestral karyotype of Cebus was then compared with that of Ateles. The rearrangements detected were 20 fusions/fissions, nine centromeric shifts, and five inversions. Atelidae species are linked by a fragmentation of chromosome 4 into three segments forming an association of 4/15, while Ateles species are linked by 13 derived associations. The results also helped clarify the content of the ancestral platyrrhine karyotype and the mode of chromosomal evolution in these primates. In particular, associations 2/16 and 5/7 should be included in the ancestral karyotype of New World monkeys.

Animals↗
PubMed1986

Genetic characterisation of the mithun (Bos frontalis) and studies of spermatogenesis, blood groups and haemoglobins of its hybrids with Bos indicus.

The mithun (Bos frontalis) and its hybrids with Bos indicus were studied to provide further cytogenetic information which might throw light on the mechanisms of the male hybrid infertility and facilitate the establishment of a stable crossbreed. It was shown that compared with conventional cattle the mithun has a homozygous, species specific 2/27 centric fusion which reduced the diploid chromosome number from 60 to 58. This provided further proof that Robertson translocation-type rearrangements have been the major source of interspecies karyotype differences in the evolution of the Bovidae. In the mithun there was also significant polymorphism between centromeres of non-homologous chromosomes and there was heteromorphism between several homologous chromosomes which could possibly serve as useful genetic markers for breeding programmes. In F1 hybrids spermatogenesis progressed to a relatively advanced stage, without going so far as to produce spermatozoa. In back crosses to B indicus spermatogenesis progressed further so that spermatozoa could be seen, though not as numerous as in normal bulls. In most hybrids there were haemoglobin bands which corresponded either to Hb A or Hb B of cattle but were much wider. It was shown that these were a combination of Hb Mi derived from the mithun and Hb A or Hb B derived from B indicus. In a few hybrids there were only Hb Mi. In these cases Hb Mi had been present in both parents and proved that the dam was not a pure siri. The possible mechanism of hybrid male infertility is discussed including faults in the epistatic gene effect between chromosomes and changes in the degree of association of centromeric regions in interspecies hybrids. It is suggested that additional cytogenetic examination of blood lymphocytes and especially of testicles would help the understanding of the fertility barriers of hybrid males and would make a breeding programme for a stable crossbreed possible.

Animals↗
PubMed1998

Evolution of annual species of the genus Medicago: a molecular phylogenetic approach.

We performed a molecular phylogenetic study based on the nuclear ribosomal internal and external transcribed spacer (ITS and ETS). Thirty-one annual Medicago species were included in the study, representing more than half of the genus and 85% of the annuals of the genus. Major incongruences were found between phylogenetic relationships and morphological classification of the genus. Morphological and cytological traits were mapped onto the phylogeny. The most parsimonious reconstruction suggested an ancestral spiny state and a recurrent transition from spiny to spineless state. From the ancestral state of 2n=16, three loss events of chromosomes must have occurred leading to the same specific number of 14 chromosomes whereas species having 30 chromosomes form a monophyletic clade.

Chromosome Deletion↗
PubMed1979

Polyploidy in fungi.

There is evidence supporting a concept of polyploid evolution in a number of groups of fungi. These typically have dominant diploid phases in their life-histories. There are a number of reports of suspected polyploidy in other fungi, but these should be considered speculative at this time.

Ascomycota↗