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1.
This study evaluated the genetic consequences of a reintroduction of the endangered annual plant Cordylanthus maritimus ssp. maritimus to Sweetwater Marsh (San Diego County, California). A survey of 21 enzyme loci in natural populations revealed that genetic diversity is very low and is primarily found as rare alleles at a few loci, making this species especially susceptible to the loss of alleles and heterozygosity through genetic drift. The reintroduction was performed in 1991 and 1992 by sowing seeds (collected from Tijuana Estuary) in numerous small patches of suitable habitat. For this study, leaf tissue was collected from all plants in all patches during flowering in 1995 and surveyed for genotype at the three enzyme loci that are polymorphic at Tijuana Estuary. Rare alleles were absent in 27 out of 30 patches for Pgm-1, in 17 out of 30 patches for Pgm-2, and in 10 out of 11 patches for Mdh-1. In all, half of the patches lacked any rare allele. Rare alleles tended to occur in patches with few individuals. Overall rare allele frequency was lower than in the colonies from which seeds were collected at two of the three loci, and heterozygosity was reduced. The Sweetwater Marsh population is at risk of losing most of its genetic variation at enzyme loci through the extinction of patches with few individuals. Future reintroduction attempts should attempt to create contiguous sets of patches or to periodically reseed existing patches to reduce the loss of genetic variation. 相似文献
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George V. Stauffer Lorraine T. Stauffer Michael D. Plamann 《Molecular & general genetics : MGG》1989,220(1):154-156
Summary A glycine cleavage enzyme system, inducible by glycine, has been demonstrated in Salmonella typhimurium. The induced enzyme levels, however, are only about 20% of the induced levels found in Escherichia coli. Starting with a serine auxotroph, mutants were isolated that grow with a serine supplement, but not with a glycine supplement. Three independently isolated mutants have reduced or nondetectable glycine cleavage enzyme levels. The new mutations, designated gcv, were mapped between the serA and lys genes at 62.5 min on the S. typhimurium chromosome.Abbreviations C1
one-carbon
- GCV
glycine cleavage
- GM
glucose minimal
- L agar
Luria agar
- LB
Luria broth
- Tc
tetracycline 相似文献
4.
Assessing the impact of episodic pollution 总被引:1,自引:0,他引:1
The increased tightening of controls on industrial and municipal wastewater discharges has resulted in steady improvements in the quality of many important rivers over recent years. However, episodic pollution, particularly from farm wastes and combined sewer overflows continues to pose a major problem, and is one of the main causes of poor quality rivers today. Despite our acknowledgement of this continuing problem, very little is known of the mechanistic basis of responses and recovery of aquatic organisms and communities exposed to intermittent pulses of common pollutants. The majority of ecotoxicological studies to date have been concerned with the effects of continuous exposure. Although such studies may provide a means of predicting the impact of episodic pollution events, a more appropriate test design would be to assess toxicity under pulsed and fluctuating exposure. Studies should also include a post-exposure observation period and should consider recovery of individuals and communities. This paper reviews the results of reported studies relevant to the investigation of episodic pollution and pays particular attention to the effects of magnitude, duration and frequency of exposure. Results of field investigations using an in situ bioassay technique are also presented to emphasize the importance of field validation of proposed water quality criteria for intermittent pollution events. 相似文献
5.
Summary Using an Escherichia coli lac deletion strain lysogenized with lambda phage carrying a metF-lacZ gene fusion (Flac), in which -galactosidase levels are dependent on metF gene expression, cis-acting mutations were isolated that affect regulation of the Salmonella typhimurium metF gene. The mutations were located in a region previously defined as the metF operator by its similarity to the E. coli metF operator sequence. Regulation of the metF gene was examined by measuring -galactosidase levels in E. coli strains lysogenized with the wild-type Flac phage and mutant Flac phage. The results suggest that the mutations disrupt the methionine control system mediated by the metJ gene product, but not the vitamin B12 control system mediated by the metH gene product. The results also demonstrate that negative control of the metF gene by the metH gene product and vitamin B12 is dependent on a functional metJ gene product.Abbreviations Ap
ampicillin
- dNTP
deoxyribonucleoside triphosphates
- GM
glucose minimal
- Km
kanamycin
- L-agar
Luria agar
- LM
lactose minimal
- SAM
s-adenosyl-L-methionine
- TPEG
phenylethyl -D-thiogalactoside
- X-gal
5-bromo-4-chloro-3-indolyl -D-galactopyranoside
- []
designates plasmid-carrier state
- ::
novel joint 相似文献
6.
Development of captive bongos (Tragelaphus eurycerus): Activity budgets and developmental milestones
Debra L. Forthman Lorraine A. Perkins Joan I. Mead Nicolette S. Miller 《Zoo biology》1992,11(3):197-207
The development of changes in visual orientation, posture, activity budgets, and behavioral milestones was examined in five bongo calves which were observed from birth to 4 or 6 months of age. The only significant change in the calves' visual orientation was an increase in orientation to food. Reclining declined significantly over weeks, while standing increased and moving did not change. Overall, stationary behaviors dominated the activity budget, but decreased significantly over the study. The category that included locomotion, object exploration, and auto-play did not change, while forage and rumination increased significantly. Contrary to expectation, the decline in suckling was not significant. Affiliative interactions with the dam decreased significantly during the study, but increases in affiliation with other bongos were not significant. Levels of agonistic behavior between the calves and their dams and other herd members were low throughout the study, and did not change significantly. One female calf achieved several developmental milestones later than the others. It is suggested that these differences may have been influenced by the dominance status of her dam. The results conform to the general developmental pattern of “hider” bovids. Bongos, however, show somewhat different patterns of social development than eland, which are reported to be more precocial in expression of aggressive and sexual behaviors. © 1992 Wiley-Liss, Inc. 相似文献
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Natural Selection VS. Random Drift: Evidence from Temporal Variation in Allele Frequencies in Nature 总被引:1,自引:1,他引:0
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We have obtained monthly samples of two species, Drosophila pseudoobscura and Drosophila persimilis, in a natural population from Napa County, California. In each species, about 300 genes have been assayed by electrophoresis for each of seven enzyme loci in each monthly sample from March 1972 to June 1975. Using statistical methods developed for the purpose, we have examined whether the allele frequencies at different loci vary in a correlated fashion. The methods used do not detect natural selection when it is deterministic (e.g., overdominance or directional selection), but only when alleles at different loci vary simultaneously in response to the same environmental variations. Moreover, only relatively large fitness differences (of the order of 15%) are detectable. We have found strong evidence of correlated allele frequency variation in 13-20% of the cases examined. We interpret this as evidence that natural selection plays a major role in the evolution of protein polymorphisms in nature. 相似文献
9.
Reminder letters and follow-up telephone calls were used to increase influenza vaccination acceptance by 273 well elderly registered at an urban community health centre. The net effect of the reminder letters was to increase overall coverage to 43%, from 17% in the previous year. Follow-up telephone calls to patients who had not responded to the letters increased coverage to only 55%. Calculation of costs per additional vaccination given revealed that the use of reminder letters alone was much more cost-effective than follow-up telephone calls in increasing coverage. However, with the current fee-for-service reimbursement by medical care insurance in Ontario, neither means of improving vaccination coverage would result in net practice earnings. The implications for an effective and efficient annual influenza program in Canada are discussed. 相似文献
10.
Theodore M. Liszczak Ph.D. Lorraine Foley Peter McL. Black 《Cell and tissue research》1986,246(2):379-385
Summary The experiments described herein use an in vitro preparation of choroid plexus to demonstrate that it is a vasopressin-responsive organ by morphologic criteria. Choroid plexus from rats was incubated for one hour in graded concentrations of arginine vasopressin (AVP). Within physiologic range of molar concentration, incubation in vasopressin induced a decrease in basal and lateral spaces in choroid plexus epithelial cells as well as an increase in number of dark cells. The number of cells with basal spaces decreased significantly from 82.7±9.2 in control tissue to 19±18 in tissue incubated in 10-12 M AVP; similarly, the number with lateral cellular spaces decreased from 20±8.8 to 7.6±2.2 cells in 10-10 M AVP. Dark cells increased in number from 3.8±2.6 in control conditions to 49±4 with 10-9 M vasopressin. These data suggest important effects of arginine vasopressin in cerebrospinal fluid (CSF) on choroid plexus, compatible with enhanced fluid transport across choroid epithelial cells. 相似文献