Evidence from sequence-tagged-site markers of a recent progenitor-derivative species pair in conifers.
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Black spruce (Picea mariana [B.S.P.] Mill.) and red spruce (Picea rubens Sarg.) are two conifer species known to hybridize naturally in northeastern North America. We hypothesized that there is a progenitor-derivative relationship between these two taxa and conducted a genetic investigation by using sequence-tagged-site markers of expressed genes. Based on the 26 sequence-tagged-site loci assayed in this study, the unbiased genetic identity between the two taxa was quite high with a value of 0.920. The mean number of polymorphic loci, the mean number of alleles per polymorphic locus, and the average observed heterozygosity were lower in red spruce (P = 35%, A(P) = 2.1, H(o) = 0.069) than in black spruce (P = 54%, A(P) = 2.9, H(o) = 0.103). No unique alleles were found in red spruce, and the observed patterns of allele distribution indicated that the genetic diversity of red spruce was essentially a subset of that found in black spruce. When considered in combination with ecological evidence and simulation results, these observations clearly support the existence of a progenitor-derivative relationship and suggest that the reduced level of genetic diversity in red spruce may result from allopatric speciation through glaciation-induced isolation of a preexisting black spruce population during the Pleistocene era. Our observations signal a need for a thorough reexamination of several conifer species complexes in which natural hybridization is known to occur. (+info)
A QTL on pig chromosome 4 affects fatty acid metabolism: evidence from an Iberian by Landrace intercross.
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Three Iberian boars were bred to 31 Landrace sows to produce 79 F1 pigs. Six F1 boars were mated to 73 F1 sows. The F2 progeny from 33 full-sib families (250 individuals) were genotyped for seven microsatellites spanning the length of chromosome 4. Least squares procedures for interval mapping were used to detect quantitative trait loci (QTL). A permutation test was used to establish nominal significance levels associated with QTL effects, and resulting probability levels were corrected to a genomewide basis. Observed QTL effects were (genomewide significance, position of maximum significance in centimorgans): percentage of linoleic acid in subcutaneous adipose tissue (< 0.01, 81); backfat thickness (< 0.01, 83); backfat weight (< 0.01, 80); longissimus muscle area (0.02, 83); live weight (0.19, 88); and percentage of oleic acid in subcutaneous adipose tissue (0.25, 81). Gene action was primarily additive. The Iberian genotypes were fatter, slower growing, and had lower linoleic and higher oleic acid contents than Landrace genotypes. The interval from 80 to 83 cM contains the FAT1 and A-FABP loci that have been shown previously to affect fat deposition in pigs. This is the first report of a QTL affecting fatty acid composition of subcutaneous adipose tissue in pigs and provides a guide for the metabolic pathways affected by candidate genes described in this region of chromosome 4. (+info)
Molecular systematics of European Hyalodaphnia: the role of contemporary hybridization in ancient species.
(75/2497)
We examined phylogenetic relationships among Daphnia using mitochondrial DNA (mtDNA) sequences from the small subunit ribosomal RNA (12S), cytochrome c oxidase subunit I and nuclear DNA sequences from the first and second internal transcribed spacer representing 1612 base positions. Phylogenetic analyses using several species of the three main Daphnia subgenera, Ctenodaphnia, Hyalodaphnia and Daphnia, revealed that the Hyalodaphnia are a monophyletic sister group of the Daphnia. Most Hyalodaphnia species occur on one continent, whereas only three are found in North America and Europe. Endemicity of species is associated with variation in thermal tolerance and habitat differentiation. Although many species of the Hyalodaphnia are known to hybridize in nature, mtDNA divergence is relatively high ca. 9%) compared to other hybridizing arthropods (ca. 3%). Reproductive isolation in Daphnia seems to evolve significantly slower than genetic isolation. We related these findings to what is known about the ecology and genetics of Daphnia in order to better understand the evolutionary diversification of lineages. The relationship of these data to phylogenetic patterns is discussed in the context of speciation processes in Daphnia. (+info)
Colony hybridization: a method for the isolation of cloned DNAs that contain a specific gene.
(76/2497)
A method has been developed whereby a very large number of colonies of Escherichia coli carrying different hybrid plasmids can be rapidly screened to determine which hybrid plasmids contain a specified DNA sequence or genes. The colonies to be screened are formed on nitrocellulose filters, and, after a reference set of these colonies has been prepared by replica plating, are lysed and their DNA is denatured and fixed to the filter in situ. The resulting DNA-prints of the colonies are then hybridized to a radioactive RNA that defines the sequence or gene of interest, and the result of this hybridization is assayed by autoradiography. Colonies whose DNA-prints exhibit hybridization can then be picked from the reference plate. We have used this method to isolate clones of ColE1 hybrid plasmids that contain Drosophila melanogaster genes for 18 and 28S rRNAs. In principle, the method can be used to isolate any gene whose base sequence is represented in an available RNA. (+info)
Quaternary constraint in hybrid of aspartate transcarbamylase containing wild-type and mutant catalytic subunits.
(77/2497)
Unusual quaternary constraint in the regulatory enzyme, aspartate transcarbamylase (aspartate carbamoyltransferase or carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2) from Escherichia coli, was demonstrated with a hybrid composed of one inactive "catalytic" subunit from a mutant strain and one active catalytic subunit and three regulatory subunits from the wild-type strain. The hybrid had a high affinity for three molecules of the bi-substrat analog, N-(phosphonacetyl)-L-aspartate, compared to the six strong binding sites in the wild-type enzyme and none in the mutant. However, the Vmax of the hybrid was only about 25% that of the wild-type enzyme. In addition, the hybrid exhibited a very low apparent affinity for the substrate, aspartate [Michaelis constant (Km) about 90 mM], as compared to the wild-type enzyme (apparent Km of 7 mM). No homotropic effect was observed for the hybrid in the absence of nucleotides as contrasted to the cooperativity of the wild-type enzyme; also, large changes in the Vmax of the hybrid were caused by the addition of the nucleotide effectors, CTP and ATP, which do not affect the Vmax of the wild-type, but influence only the cooperativity and the apparent Km. Although the hybrid undergoes a ligand-promoted conformational change analogous to that of the wild-type enzyme, this transition required a 20-fold higher concentration of the substrate analog, succinate. It appears that the "paralysis" of the wild-type catalytic subunit in the hybrid can be attributed to subunit interactions which constrain the molecule in a low-affinity state. (+info)
Biochemical construction and selection of hybrid plasmids containing specific segments of the Escherichia coli genome.
(78/2497)
Using a poly(dA-dT) "connector" method, a population of annealed hybrid circular DNAs was constructed in vitro; each hybrid DNA circle containing one full-length molecule of poly(dT)-tailed DNA from E1 colicinogenic factor (Col E1) fragmented by EcoRI endonuclease annealed to any one of a collection of poly(dA)-tailed linear DNA fragments of the entire E. coli genome. This annealed, but unligated, hybrid DNA was used to transform several different auxotrophic mutants of E. coli, and by direct selection, bacterial clones were isolated which contained specific hybrid plasmids. In this manner, bacterial strains containing Col E1 hybrid plasmids carrying the entire tryptophan operon or the arabinsoe and leucine operons were isolated. The methods described should allow the molecular cloning of any portion of the E. coli genome by selection from a pool of DNA molecules containing at least several hundred different hybrids representing the entire bacterial genome. (+info)
Ineffectiveness of Vi and chemically treated endotoxins as typhoid vaccines in mice challenged with a Salmonella typhosa-Salmonella typhimurium hybrid.
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Purified Vi antigen, acetic anthydride-treated Salmonella typhosa endotoxin, and potassium methylate-treated S. typhosa endotoxin employed as vaccines in Swiss white mice failed to protect these animals against challenge with a virulent S. typhimurium hybrid expressing S. typhosa antigens. (+info)
Construction of intergeneric hybrids using bacteriophage P1CM: transfer of the Klebsiella aerogenes ribitol dehydrogenase gene to Escherichia coli.
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Study of many of the interesting properties of Klebsiella aerogenes is limited by the lack of a well-characterized genetic system for this organism. Our investigations of the evolution of the enzyme ribitol dehydrogenase (EC 1.1.1.56) in K. aerogenes would be greatly facilitated by the availability of such a system, and we here report two approaches to developing one. We have isolated mutants sensitive to the coliphage P1, which will efficiently tranduce genetic markers between such sensitive strains and which will thus make detailed mapping studies possible. Derivatives of K. aerogenes lysogenic for P1 can be readily isolated by using the specialized transducing particle P1CMclr100. Bacteria lysogenic for this phage are chloramphenicol resistant and temperature sensitive. Phage particles produced by temperature induction of such lysogens can be used to transfer K. aerogenes genes to the natural host of P1 phage. Escherichia coli. We have used this method to prepare derivatives of E. coli K-12 carrying the K. aerogenes genes conferring the ability to metabolize the pentitols ribitol and D-arabitol. We have shown that these E. coli-K. aerogenes hybrids synthesize a ribitol dehydrogenase with the properties of the K. aerogenes enzyme and have mapped the position of the transferred gene on the E. coli chromosome. The ramifications of this methodology are discussed. (+info)