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At least 883 records · Page 49Linked to original sources
PubMed1976

Interspecific "common" repetitive DNA sequences in salamanders of the genus Plethodon.

Intermediate repetitive sequences of Plethodon cinereus which comprised about 30% of the genomic DNA were isolated and iodinated with 125I. About 5% of the 125I-repetitive fraction hybridized with a large excess of DNA from P. dunni at Cot 20. About half of the 125I-DNA in the hybrids was resistant to extensive digestion with S-1 nuclease. The average molecular size of the S-1 nuclease-resistant fraction was about 100 nucleotide pairs. The melting temperature of the S-1 nuclease-resistant fraction was about 2 degrees lower than that of the corresponding fraction made with P. cinereus DNA. These results are taken to indicate the presence in the genomes of P. cinereus and P. dunni of evolutionarily stable "common" repetitive sequences. The average frequency of repetition of the common repetitive sequences is about 6,000 X in both species. The common repetitive fraction is also present in the genomes of other species of Plethodon, although the general populations of intermediate repetitive sequences are markedly different from one species to another. The cinereus--dunni common repetitive sequences could not be detected in plethodontids belonging to different tribes, nor in more distantly related amphibians. The profiles of binding of the common repetitive sequences to CsCl or CS2SO4-Ag+ density gradient fractions of P. dunni DNA suggested that these sequences consisted of heterogeneous components with respect to base compositions, and that they did not include large amounts of the genes for ribosomal RNA, 5S RNA, 4S RNA, or histone messenger RNA. In situ hybridization of the 3H-labelled intermediate repetitive sequences of P. cinereus to male meiotic chromosomes of the same species gave autoradiographs after an exposure of seven days showing all 14 chromosomes labelled. The pattern of labelling appeared not to be random, but was impossible to analyse on account of the irregular shapes and different degrees of stretching of diplotene and prometaphase chromosomes. In situ hybridization of the same sequences to meiotic chromosomes from P. dunni gave autoradiographs after 60 d exposure in which all chromosomes were labelled. These heterologous in situ hybrids can only have involved the "common" repetitive sequences.

Amphibians↗
PubMed1977

An investigation of some problems concerning nucleolus organizers in salamanders.

Observed differences in the sizes of lampbrush nucleolus organizers in Plethodon cinereus have been shown by in situ hybridization to reflect true molecular differences in the numbers of ribosomal cistrons located at these organizers. Likewise, from in situ hybridization experiments on lampbrush and spermatocyte chromosomes it has been shown that animals may be, and indeed usually are, heterozygous with respect to the numbers of ribosomal cistrons on each half of the nucleolus bivalent. Filter hybridizations carried out on 33 males from a New Jersey population and 20 males from a Connecticut population have shown a 7.5-fold range in the numbers of ribosomal cistrons per diploid cell in the New Jersey population, and a 2.5-fold range in the Connecticut population. In view of the general heterozygosity of nucleolus organizers in these animals, the actual range in nucleolus organizer sizes in the New Jersey population is estimated to be at least 15-fold.

Animals↗
PubMed1976

In situ hybridization of "nick-translated" 3H-ribosomal DNA to chromosomes from salamanders.

A technique is described for preparation of 3H-labelled DNA by nick-translation employing deoxyribonuclease I and DNA polymerase I. The labelled DNA can be obtained in high yield with specific activities of 10(6) cpm/mug or more. Ribosomal DNA, isolated from ovaries of young Xenopus laevis, and whole DNA from Plethodon cinereus were labelled in this way. The rDNA was used for in situ hybridization to meiotic chromosomes from P. cinereus, P. vehiculum and P. dunni. Autoradiographs of in situ hybrids were exposed for 5 to 10 days, by which time nucleolus organizer regions on the chromosomes of all 3 species were clearly and specifically labelled. In all cases, labelling was confined to a short region near the middle of the short arm of both halves of a medium length bivalent. It is concluded that nick-translation is a useful and altogether efficient method of labelling nucleic acids for subsequent use in experiments involving in situ hybridizations.

Animals↗
PubMed1976

Erythrocyte enzyme activities in diploid and triploid salamanders (Pleurodeles waltlii) of both sexes.

Studies of several enzyme activities and of some metabolites in erythrocytes of the newt Pleurodels waltilii are described. The results indicate that differences exist between enzyme activities in males and females and in diploid and triploid animals. Females have higher erythrocyte enzyme activities than males. However, triploid animals have lower enzyme activites in their erythrocytes than diploid animals; this observation is more striking in females than in males.

Alleles↗
PubMed1976

Genetic variation in two widespread species of salamanders, Taricha granulosa and Taricha torosa.

Two species of the genus Taricha are widely distributed. T. granulosa ranges from southern Alaska to central California. T. torosa is comprised of two described subspecies, T. t. torosa, which occupies much of the coast ranges of California, and T. t. sierrae, which inhabits the western slopes of the Sierra Nevada Mountains. A starch gel electrophoretic survey for genetic variation at 34 loci in four population samples of T. granulosa and at 40 loci in five population samples of T. torosa reveals differences among these taxa both in amounts of intrapopulational variability and in patterns of geographic variation. Average observed heterozygosity is 9.6% +/- 0.3% in T. granulosa, 3.3% +/- 0.5% in T. t. torosa, and 7.2% +/- 1.2% in T. t. sierrae. Average numbers of alleles per lon T. t. sierrae, and lowest in T. t. torosa. Oregon and California granulosa are genetically nearly as different as the subspecies of torosa, but geographic variation is continuous in the former. T. torosa on the other hand is comprised of three distinct gene pools--T. t. sierrae and northern and southern races of T. t. torosa. Strikingly different amounts of intrapopulational genetic variation and patterns of geographic variation may be explained by steady-state species differences, but historical causes may also exist.

Animals↗