Ribosomal DNA variation within and between species of rodents, with emphasis on the genus Onychomys

Molecular phylogeny and species delimitation of the genus Tonkinacris (Orthoptera, Acrididae, Melanoplinae) from China

Tonkinacris is a small group in Acrididae. While a few species were occasionally sampled in some previous molecular studies, there is no revisionary research devoted to the genus. In this study, we explored the phylogeny of and the relationships among Chinese species of the genus Tonkinacris using the mitochondrial COI barcode and the complete sequences of ITS1 and ITS2 of the nuclear ribosomal DNA. The phylogeny was reconstructed in maximum likelihood and Bayesian inference frameworks, respectively. The overlap range between intraspecific variation and interspecific divergence was assessed via K2P distances. Species boundaries were delimitated using phylogenetic species concept, NJ tree, K2P distance, the statistical parsimony network as well as the GMYC model. The results demonstrate that the Chinese Tonkinacris species is a monophyletic group and the phylogenetic relationship among them is (T. sinensis, (T. meridionalis, (T. decoratus, T. damingshanus))). While T. sinensis, T. meridionalis and T. decoratus were confirmed being good independent species strongly supported by both morphological and molecular evidences, the validity of T. damingshanus was not perfectly supported by molecular evidence in this study.

Intragenomic variation in ribosomal RNA gene of the sea urchin Lytechinus variegatus

The first series of studies on the rDNA satellite of the sea urchin, Lytechinus variegatus, based on saturation hybridization of rRNA-rDNA and renaturation kinetics, showed that repeat length of rRNA gene was of about 8 kb in which there was no provision for NTS. The EM denaturation mapping, however, revealed (1) that the gene was 75% larger (longer) than 8 kb, within which there was a NTS whose length varied in repeating units, (3) and there was a region of high GC almost in the middle of the transcribed part. The suggestion of length and sequential heterogeneity in the gene copies coming from the first denaturation mapping prompted further studies with techniques so that the conclusions of the previous results could be stated with finality. The results that emanated from further studies established that the rDNA repeat length of L. variegatus was of about 12 kb and that the NTS ranged from 3.8 to 6.4 kb. Earlier demonstration of a moderately high-GC segment within the transcribed part was also confirmed by sequence analysis. However, the stipulations on the NTS regarding sequential and length heterogeneity, still awaits elucidation by sequence analysis.

Phylogenetic relationships among Homo sapiens and related species based on restriction site variations in rDNA spacers

A rapid method, using 12 restriction enzymes, was employed to analyze variations in ribosomal DNA (rDNA) spacers in a study of phylogenetic relationships between Homo sapiens and related species. We mapped restriction sites in the external and internal spacer regions and compared the arrangements of sites. The estimated sequence divergence between Homo sapiens and Pan troglodytes, Pan paniscus, Gorilla gorilla, Pongo pygmaeus, Hylobates lar, H. agilis, and Macaca fuscata was 2.7, 2.3, 3.8, 7.3, 6.8, 7.8, and 14.1%, respectively. The genetic relationships inferred from these distances generally correspond to those inferred from analyses of other molecular markers in the literature. The divergence between H. lar and H. agilis and between H. lar and H. syndactylus was 0.34 and 2.4%, respectively.