Temporal variation in the ribosomal DNA nontranscribed spacer of Aedes albopictus (Diptera: Culicidae)

Genome ◽  
1991 ◽  
Vol 34 (2) ◽  
pp. 293-297 ◽  
Author(s):  
Srinivas Kambhampati ◽  
Karamjit S. Rai
Keyword(s):  
Temporal Variation ◽  
Aedes Albopictus ◽  
Ribosomal Dna ◽  
Population Variation ◽  
High Rate ◽  
Length Variation ◽  
Spacer Length ◽  
Nontranscribed Spacer ◽  
Population Component ◽  
Different Populations

Length variation in ribosomal DNA (rDNA) nontranscribed spacer within and among populations of the mosquito Aedes albopictus was studied over a 3-year period in eight different populations from Texas. Statistically significant variation was detected among populations at each sampling date. Significant, but nondirectional, changes were observed within populations over time. An average of 78% of the total variance in the frequencies of spacer variants was attributable to the within-population component, suggesting local differentiation. The results corroborate those from a previous study on spacer length diversity in populations of A. albopictus from around the world and are similar to those from a study on temporal variation in allozyme frequencies in some of the same populations and sampling dates. We propose that a high rate of production of length variants and localized breeding structure could explain the observed high levels of within- and among-population variation in A. albopictus.Key words: rDNA, nontranscribed spacer, genetic structure, temporal variation, Aedes albopictus.

A comparative analysis of genetic polymorphism in wild and cultivated barley from Tibet using isozyme and ribosomal DNA markers

Genome ◽  
1994 ◽  
Vol 37 (4) ◽  
pp. 631-638 ◽  
Author(s):  
Qifa Zhang ◽  
G. P. Yang ◽  
Xiankai Dai ◽  
J. Z. Sun
Keyword(s):  
Genetic Variation ◽  
Ribosomal Dna ◽  
Wild Barley ◽  
Length Variation ◽  
Spacer Length ◽  
Origin And Evolution ◽  
Centre Of Diversity ◽  
Esterase Loci ◽  
Cultivated Barley ◽  
Comparison Of The Results

This study was conducted to address some of the issues concerning the possible significance of Tibet in the origin and evolution of cultivated barley. A total of 1757 barley accessions from Tibet, including 1496 entries of Hordeum vulgare ssp. vulgare (HV), 229 entries of the six-rowed wild barley H. vulgare ssp. agriocrithon (HA), and 32 entries of the two-rowed wild barley H. vulgare ssp. spontaneum (HS), were assayed for allozymes at four esterase loci. A subsample of 491 accessions was surveyed for spacer-length polymorphism at two ribosomal DNA loci. Genetic variation is extensive in these barley groups, and the amount of genetic diversity in cultivated barley of this region is comparable with that of cultivated barley worldwide. The level of genetic variation of HA is significantly lower than the other two barley groups, and there is also substantial heterogeneity in the level of polymorphism among different agrigeographical subregions. However, little genetic differentiation was detected among the three barley groups (HV, HA, and HS), as well as among different agrigeographical subregions. Comparison of the results from this and previous studies indicated a strong differentiation between Oriental and Occidental barley, thus favoring the hypothesis of a diphyletic origin of cultivated barley.Key words: Hordeum, allozyme, rDNA spacer-length variation, centre of diversity, phylogeny.

Ribosomal DNA spacer-length variation inSecale spp. (Poaceae)

1990 ◽  
Vol 171 (1-4) ◽  
pp. 205-220 ◽  
Author(s):  
P. Reddy ◽  
R. Appels ◽  
B. R. Baum
Keyword(s):  
Ribosomal Dna ◽  
Length Variation ◽  
Spacer Length

Variation of the intergenic spacer region of ribosomal DNA in cultivated and wild rice species

Genome ◽  
1990 ◽  
Vol 33 (2) ◽  
pp. 209-218 ◽  
Author(s):  
Y. Sano ◽  
R. Sano
Keyword(s):  
Ribosomal Dna ◽  
Intergenic Spacer ◽  
Length Variation ◽  
Cultivated Rice ◽  
Spacer Length ◽  
Intergenic Spacer Region ◽  
Wild Rice Species ◽  
Cultivated Species ◽  
Restriction Enzyme Maps ◽  
Spacer Length Variants

Spacer-length variation in ribosomal DNA (rDNA) was surveyed in two cultivated rice species and their wild relatives. Among 243 accessions observed, 18 different spacer-length variants were detected. Length heterogeneity was found within and among species as well as within individuals. Conventional genetic analysis revealed that two spacer-length variants were located at two unlinked loci. Restriction enzyme maps showed that length heterogeneity resulted from repetition of short repeated sequences in the intergenic spacer region in the Asian cultivar and its progenitor; however, the spacer region greatly differed from those of reproductively isolated taxa with respect to the length and the sequence. Furthermore, the Asian cultivated species and its progenitor were highly polymorphic for rDNA spacer-length variation and they were differentiated in frequencies of spacer-length variants as well as varietal groups within the cultivated species. Asian cultivars tended to carry homogeneous repeats of rDNA compared with their progenitor, suggesting different forms of homogenization occurring in Asian cultivars.Key words: ribosomal DNA, intergenic spacer, polymorphism, inheritance, Oryza.

scholarly journals Evolution of the Ribosomal DNA Spacers of Drosophila melanogaster: Different Patterns of Variation on X and Y Chromosomes

Genetics ◽  
1987 ◽  
Vol 116 (2) ◽  
pp. 225-232
Author(s):  
Scott M Williams ◽  
Glenn R Furnier ◽  
Eric Fuog ◽  
Curtis Strobeck
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Selection ◽  
Ribosomal Dna ◽  
Genomic Dna ◽  
Restriction Enzymes ◽  
Ribosomal Gene ◽  
Length Variation ◽  
Spacer Length ◽  
Y Chromosomes ◽  
The World

ABSTRACT Length variation of the ribosomal gene spacers of Drosophila melanogaster was studied. Analysis of 47 X chromosomal and 47 Y chromosomal linked rDNA arrays collected from five continents indicates that the arrays on the two chromosomes differ qualitatively. The Y-linked arrays from around the world share little or no similarity for either their overall length or the organization of their spacers. Most of the X-linked arrays do, however, share a major length spacer of 5.1 kb. In addition, those X-linked arrays that have a major 5.1-kb band have similar spacer organization as demonstrated by genomic DNA digestions with several restriction enzymes. These data strongly support the hypothesis that spacer length patterns on only X-linked genes are maintained primarily by natural selection.

scholarly journals Patterns of variation in the rDNA cistron within and among world populations of a mosquito, Aedes albopictus (Skuse).

Genetics ◽  
1989 ◽  
Vol 121 (3) ◽  
pp. 539-550
Author(s):  
W C Black ◽  
D K McLain ◽  
K S Rai
Keyword(s):  
Aedes Albopictus ◽  
Local Population ◽  
Population Level ◽  
Restriction Map ◽  
Repeat Region ◽  
Molecular Drive ◽  
Nontranscribed Spacer ◽  
Coding Regions ◽  
The World ◽  
Ribosomal Cistron

Abstract A restriction map was constructed of the ribosomal cistron in a mosquito, Aedes albopictus (Skuse). The 18s, 28s and nontranscribed spacer (NTS) regions were subcloned and used to probe for intraspecific variation. Seventeen populations were examined throughout the world range of the species. No variation was detected in the coding regions but extensive and continuous variation existed in the NTS. The NTS consisted of two nonhomologous regions. The first region contained multiple 190-bp AluI repeats nested within larger XhoI repeats of various sizes. There was a large number of length variants in the AluI repeat region of the NTS. No repeats were found in the second region and it gave rise to relatively fewer variants. An analysis of NTS diversity in individual mosquitoes indicated that most of the diversity arose at the population level. Discriminant analysis was performed on spacer types in individual mosquitoes and demonstrated that individuals within a population carried a unique set of spacers. In contrast with studies of the NTS in Drosophila populations, there seems to be little conservation of spacers in a population. The importance of molecular drive relative to drift and selection in the generation of local population differentiation is discussed.

scholarly journals Temporal variation of wing geometry in Aedes albopictus

2012 ◽  
Vol 107 (8) ◽  
pp. 1030-1034 ◽  
Author(s):  
Paloma Oliveira Vidal ◽  
Eneas Carvalho ◽  
Lincoln Suesdek
Keyword(s):  
Temporal Variation ◽  
Aedes Albopictus ◽  
Wing Geometry

Initiation and termination of DNA replication in human rRNA genes

1993 ◽  
Vol 13 (10) ◽  
pp. 6600-6613
Author(s):  
R D Little ◽  
T H Platt ◽  
C L Schildkraut
Keyword(s):  
Dna Replication ◽  
Ribosomal Dna ◽  
Regulatory Elements ◽  
Transcription Unit ◽  
Replication Initiation ◽  
Rrna Genes ◽  
Rrna Gene ◽  
Replication Forks ◽  
Nontranscribed Spacer ◽  
Dna Repeat

We have used the multicopy human rRNA genes as a model system to study replication initiation and termination in mammalian chromosomes. Enrichment for replicating molecules was achieved by isolating S-phase enriched populations of cells by centrifugal elutriation, purification of DNA associated with the nuclear matrix, and a chromatographic procedure that enriches for molecules containing single-stranded regions, a characteristic of replication forks. Two-dimensional agarose gel electrophoresis techniques were used to demonstrate that replication appears to initiate at multiple sites throughout most of the 31-kb nontranscribed spacer (NTS) of human ribosomal DNA but not within the 13-kb transcription unit or adjacent regulatory elements. Although initiation events were detected throughout the majority of the NTS, some regions may initiate more frequently than others. Termination of replication, the convergence of opposing replication forks, was found throughout the ribosomal DNA repeat units, and, in some repeats, specifically at the junction of the 3' end of the transcription unit and the NTS. This site-specific termination of replication is the result of pausing of replication forks near the sites of transcription termination. The naturally occurring multicopy rRNA gene family offers a unique system to study mammalian DNA replication without the use of chemical synchronization agents.

scholarly journals Isolation and Characterization of Proteolytic Ruminal Bacteria from Sheep and Goats Fed the Tannin-Containing Shrub Legume Calliandra calothyrsus

1999 ◽  
Vol 65 (7) ◽  
pp. 3075-3083 ◽  
Author(s):  
Christopher S. McSweeney ◽  
Brian Palmer ◽  
Rowan Bunch ◽  
Denis O. Krause
Keyword(s):  
Ribosomal Dna ◽  
Condensed Tannin ◽  
High Rate ◽  
Calliandra Calothyrsus ◽  
Polymorphism Analysis ◽  
Ruminal Bacteria ◽  
Sheep And Goats ◽  
16S Ribosomal Dna ◽  
Isolation And Characterization ◽  
High Specific Growth Rate

ABSTRACT Tannins in forages complex with protein and reduce the availability of nitrogen to ruminants. Ruminal bacteria that ferment protein or peptides in the presence of tannins may benefit digestion of these diets. Bacteria from the rumina of sheep and goats fed Calliandra calothyrsus (3.6% N and 6% condensed tannin) were isolated on proteinaceous agar medium overlaid with either condensed (calliandra tannin) or hydrolyzable (tannic acid) tannin. Fifteen genotypes were identified, based on 16S ribosomal DNA-restriction fragment length polymorphism analysis, and all were proteolytic and fermented peptides to ammonia. Ten of the isolates grew to high optical density (OD) on carbohydrates (glucose, cellobiose, xylose, xylan, starch, and maltose), while the other isolates did not utilize or had low growth on these substrates. In pure culture, representative isolates were unable to ferment protein that was present in calliandra or had been complexed with tannin. One isolate, Lp1284, had high protease activity (80 U), a high specific growth rate (0.28), and a high rate of ammonia production (734 nmol/min/ml/OD unit) on Casamino Acids and Trypticase Peptone. Phylogenetic analysis of the 16S ribosomal DNA sequence showed that Lp1284 was related (97.6%) to Clostridium botulinum NCTC 7273. Purified plant protein and casein also supported growth of Lp1284 and were fermented to ammonia. This is the first report of a proteolytic, ammonia-hyperproducing bacterium from the rumen. In conclusion, a diverse group of proteolytic and peptidolytic bacteria were present in the rumen, but the isolates could not digest protein that was complexed with condensed tannin.

scholarly journals Organization of replication of ribosomal DNA in Saccharomyces cerevisiae.

1988 ◽  
Vol 8 (11) ◽  
pp. 4927-4935 ◽  
Author(s):  
M H Linskens ◽  
J A Huberman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Ribosomal Dna ◽  
Repeat Unit ◽  
Replication Forks ◽  
Sequence Element ◽  
Autonomously Replicating Sequence ◽  
Nontranscribed Spacer ◽  
Precursor Rna ◽  
Mapping Techniques ◽  
Region Ii

Using recently developed replicon mapping techniques, we have analyzed the replication of the ribosomal DNA in Saccharomyces cerevisiae. The results show that (i) the functional origin of replication colocalizes with an autonomously replicating sequence element previously mapped to the nontranscribed spacer region, (ii) only a fraction of the potential origins are utilized in a single S phase, and (iii) the replication forks moving counter to the direction of transcription of the 37S precursor RNA stop at or near the termination site of transcription. Consequently, most ribosomal DNA is replicated unidirectionally by forks moving in the direction of transcription and most replicons are larger than the repeat unit. The significance of this finding for the replication of abundantly transcribed genes is discussed.

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