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51.
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53.
The alcohol dehydrogenase (Adh) region from five planitibia subgroup
species of Hawaiian picture-wing Drosophila has been cloned. A total of 15
kb of DNA in and around the Adh gene has been compared among the five
species. Genetic distances were calculated to determine evolutionary
relationships. These distances agree with previous distances determined by
protein polymorphism and DNA hybridization techniques and can be
interpreted in terms of specific island colonization and speciation
(founder) events over the past 5 Myr. Examination of the restriction maps
of the cloned Adh region from the five species shows many instances of
small deletions, insertion of a transposable element in D. heteroneura, and
the existence of a highly variable region on the 3' side of the Adh gene.
Clustering relationships and rates of DNA change are calculated and
compared with the relationship found for other species of Drosophila.
相似文献
54.
Maize (Zea mays L.) tortilla is the major staple food for the Mexican population. Nine tropical maize genotypes were evaluated. All samples had white grains, a common characteristic in tropical maize, and therefore they were appropriate for nixtamalized flour industry. Grain, flour, masa and tortilla characteristics of each maize genotype were evaluated. Length, width, thickness, weight of 1000 grains and hardness of grain were determined. Moisture content, proteins, fat, ash, mean particle size, water absorption index, enthalpy, and flour temperature were also evaluated. Adhesiveness and cohesiveness were evaluated in masa. Moisture content, protein, capacity to puff up, roll making, tension and cutting strength were determined in tortillas. There were significant differences (p≤0.05) in most of the evaluated characteristics. Grain length values varied between 9.26 and 11.02 mm for populations 23 and 22, respectively. Grain hardness oscillated between 11.17 (population 32) and 14.75 (landrace Mejen). According to the weight of 1000 grains most genotypes had small grains. The minimum and maximum moisture values of flour and tortillas were 8.33-9.99% and 46.20-50.36%, respectively. The texture of tortillas elaborated from population 32 and landrace Mejen had the lowest tension and cutting strength, resulting the best genotypes for making tortilla. 相似文献
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56.
Beneficial effect of fluorocarbon emulsion media on the function of neuromuscular preparations in vitro
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The effects of liquid fluorocarbons as bathing media were determined by use of in vitro neuromuscular preparations. Rat hemidiaphragms were bathed in either oxygenated fluorocarbon (FC) emulsion or standard oxygenated Krebs solution. Contractile force in response to simple supramaximal nerve stimuli as well as to high frequency stimulation was greater, while twitch:tetanus ratio was smaller in FC emulsion. With such medium, post-tetanic potentiation of contraction was also more consistently observed. Indirectly stimulated diaphragms survived longer in FC emulsion. After cessation of oxygenation, oxygen tension (ρO(2)) of the medium declined more rapidly with Krebs than with FC emulsion; ρO(2) directly correlated with force of contraction. Similarly, in the chick biventer cervicis preparation, FC emulsion enhanced nerve-stimulated force of contraction; returning the preparation to standard Krebs solution reversed this phenomenon. Dose-resonse curves of muscle contraction in response to acetycholine and KCl administration were shifted upward during FC emulsion superfusion. Frequency of miniature endplate potentials was lower in FC emulsion than that observed in Krebs solution, measured from the same cell of the rat diaphragm. Resting membrane potentials were also greater in muscle cells sampled from FC emulsion-bathed preparations. These data suggest that FC emulsion is superior to standard Krebs solution as a bathing medium for in vitro neuromuscular preparations by virtue of the high solubility of oxygen in it. 相似文献
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58.
Kuzoff RK; Sweere JA; Soltis DE; Soltis PS; Zimmer EA 《Molecular biology and evolution》1998,15(3):251-263
18S ribosomal RNA genes are the most widely used nuclear sequences for
phylogeny reconstruction at higher taxonomic levels in plants. However, due
to a conservative rate of evolution, 18S rDNA alone sometimes provides too
few phylogenetically informative characters to resolve relationships
adequately. Previous studies using partial sequences have suggested the
potential of 26S or large-subunit (LSU) rDNA for phylogeny retrieval at
taxonomic levels comparable to those investigated with 18S rDNA. Here we
explore the patterns of molecular evolution of entire 26S rDNA sequences
and their impact on phylogeny retrieval. We present a protocol for PCR
amplification and sequencing of entire (approximately 3.4 kb) 26S rDNA
sequences as single amplicons, as well as primers that can be used for
amplification and sequencing. These primers proved useful in angiosperms
and Gnetales and likely have broader applicability. With these protocols
and primers, entire 26S rDNA sequences were generated for a diverse array
of 15 seed plants, including basal eudicots, monocots, and higher eudicots,
plus two representatives of Gnetales. Comparisons of sequence dissimilarity
indicate that expansion segments (or divergence domains) evolve 6.4 to 10.2
times as fast as conserved core regions of 26S rDNA sequences in plants.
Additional comparisons indicate that 26S rDNA evolves 1.6 to 2.2 times as
fast as and provides 3.3 times as many phylogenetically informative
characters as 18S rDNA; compared to the chloroplast gene rbcL, 26S rDNA
evolves at 0.44 to 1.0 times its rate and provides 2.0 times as many
phylogenetically informative characters. Expansion segment sequences
analyzed here evolve 1.2 to 3.0 times faster than rbcL, providing 1.5 times
the number of informative characters. Plant expansion segments have a
pattern of evolution distinct from that found in animals, exhibiting less
cryptic sequence simplicity, a lower frequency of insertion and deletion,
and greater phylogenetic potential.
相似文献
59.
CA Istock JA Bell N Ferguson NL Istock 《Journal of industrial microbiology & biotechnology》1996,17(3-4):137-150
A discussion of the species problem in modern evolutionary biology serves as the point of departure for an exploration of how the basic science aspects of this problem relate to efforts to map bacterial diversity for practical pursuits—for prospecting among the bacteria for useful genes and gene-products. Out of a confusing array of species concepts, the Cohesion Species Concept seems the most appropriate and useful for analyzing bacterial diversity. Techniques of allozyme analysis and DNA fingerprinting can be used to put this concept into practice to map bacterial genetic diversity, though the concept requires minor modification to encompass cases of complete asexuality. Examples from studies of phenetically definedBacillus species provide very partial maps of genetic population structure. A major conclusion is that such maps frequently reveal deep genetic subdivision within the phenetically defined specles; divisions that in some cases are clearly distinct genetic species. Knowledge of such subdivisions is bound to make prospecting within bacterial diversity more effective. Under the general concept of genetic cohesion a hypothetical framework for thinking about the full range of species conditions that might exist among bacteria is developed and the consequences of each such model for species delineation, and species identification are discussed. Modes of bacterial evolution, and a theory of bacterial speciation with and without genetic recombination, are examined. The essay concludes with thoughts about prospects for very extensive mapping of bacterial diversity in the service of future efforts to find useful products. In this context, evolutionary biology becomes the handmaiden of important industrial activities. A few examples of past success in commercializing bacterial gene-products from species ofBacillus and a few other bacteria are reviewed. 相似文献
60.
Vessel diameters and branching angles are measured from a large number of arterial bifurcations in the retina of a normal human subject and in that of a rhesus monkey. The results are compared with each other and with theoretical results on this subject. 相似文献