Extensive amino acid polymorphism at the pgm locus is consistent with adaptive protein evolution in Drosophila melanogaster.
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PGM plays a central role in the glycolytic pathway at the branch point leading to glycogen metabolism and is highly polymorphic in allozyme studies of many species. We have characterized the nucleotide diversity across the Pgm gene in Drosophila melanogaster and D. simulans to investigate the role that protein polymorphism plays at this crucial metabolic branch point shared with several other enzymes. Although D. melanogaster and D. simulans share common allozyme mobility alleles, we find these allozymes are the result of many different amino acid changes at the nucleotide level. In addition, specific allozyme classes within species contain several amino acid changes, which may explain the absence of latitudinal clines for PGM allozyme alleles, the lack of association of PGM allozymes with the cosmopolitan In(3L)P inversion, and the failure to detect differences between PGM allozymes in functional studies. We find a significant excess of amino acid polymorphisms within D. melanogaster when compared to the complete absence of fixed replacements with D. simulans. There is also strong linkage disequilibrium across the 2354 bp of the Pgm locus, which may be explained by a specific amino acid haplotype that is high in frequency yet contains an excess of singleton polymorphisms. Like G6pd, Pgm shows strong evidence for a branch point enzyme that exhibits adaptive protein evolution. (+info)
Linkage disequilibria and the site frequency spectra in the su(s) and su(w(a)) regions of the Drosophila melanogaster X chromosome.
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Over the last decade, surveys of DNA sequence variation in natural populations of several Drosophila species and other taxa have established that polymorphism is reduced in genomic regions characterized by low rates of crossing over per physical length. Parallel studies have also established that divergence between species is not reduced in these same genomic regions, thus eliminating explanations that rely on a correlation between the rates of mutation and crossing over. Several theoretical models (directional hitchhiking, background selection, and random environment) have been proposed as population genetic explanations. In this study samples from an African population (n = 50) and a European population (n = 51) were surveyed at the su(s) (1955 bp) and su(w(a)) (3213 bp) loci for DNA sequence polymorphism, utilizing a stratified SSCP/DNA sequencing protocol. These loci are located near the telomere of the X chromosome, in a region of reduced crossing over per physical length, and exhibit a significant reduction in DNA sequence polymorphism. Unlike most previously surveyed, these loci reveal substantial skews toward rare site frequencies, consistent with the predictions of directional hitchhiking and random environment models and inconsistent with the general predictions of the background selection model (or neutral theory). No evidence for excess geographic differentiation at these loci is observed. Although linkage disequilibrium is observed between closely linked sites within these loci, many recombination events in the genealogy of the sampled alleles can be inferred and the genomic scale of linkage disequilibrium, measured in base pairs between sites, is the same as that observed for loci in regions of normal crossing over. We conclude that gene conversion must be high in these regions of low crossing over. (+info)
Molecular population genetics of male accessory gland proteins in Drosophila.
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Drosophila seminal proteins have an unusually high rate of molecular sequence evolution, suggesting either a high rate of neutral substitution or rapid adaptive evolution. To further quantify patterns of polymorphism and divergence in genes encoding seminal proteins, also called accessory gland proteins (Acp's), we conducted a sequencing survey of 10 Acp genes in samples of Drosophila melanogaster and D. simulans (Acp29AB, Acp32CD, Acp33A, Acp36DE, Acp53Ea, Acp62F, Acp63F, Acp76A, Acp95EF, and Acp98AB). Mean heterozygosity at replacement sites in D. simulans was 0.0074 for Acp genes and 0.0013 for a set of 19 non-Acp genes, and mean melanogaster-simulans divergence at replacement sites was 0.0497 for Acp genes and 0.0107 at non-Acp genes. The elevated divergence of Acp genes is thus accompanied by elevated within-species polymorphism. In addition to the already-reported departures of Acp26A, Acp29AB, and Acp70A from neutrality, our data reject neutrality at Acp29AB and Acp36DE in the direction of excess replacements in interspecific comparisons. (+info)
How do countries regulate the health sector? Evidence from Tanzania and Zimbabwe.
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The health sectors in many low- and middle-income countries have been characterized in recent years by extensive private sector activity. This has been complemented by increasing public-private linkages, such as the contracting-out of selected services or facilities, development of new purchasing arrangements, franchising and the introduction of vouchers. Increasingly, however, experience with the private sector has indicated a number of problems with the quality, price and distribution of private health services, and thus led to a growing focus on the role of government in regulation. This paper presents the existing network of regulations governing private activity in the health sectors of Tanzania and Zimbabwe, and their appropriateness in the context of emerging market realities. It draws on a comparative mapping exercise reviewing the complexity of the variables currently being regulated, the level of the health system at which they apply, and the specific instruments being used. Findings indicate that much of the existing regulation occurs through legislation. There is still very much a focus on the 'social' rather than 'economic' aspects of regulation within the health sector. Recent changes have attempted to address aspects of private health provision, but some very key gaps remain. In particular, current regulations in Tanzania and Zimbabwe: (1) focus on individual inputs rather than health system organizations; (2) aim to control entry and quality rather than explicitly quantity, price or distribution; and (3) fail to address the market-level problems of anti-competitive practices and lack of patient rights. This highlights the need for additional measures to promote consumer protection and address the development of new private markets such as for health insurance or laboratory and other ancillary services. (+info)
Do they work? Regulating for-profit providers in Zimbabwe.
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The experience of low- and middle-income countries (LMC) with respect to regulation and legislation in the health sector is in marked contrast to that of Canada and Europe. It is suggested that the degree to which regulatory mechanisms can influence private sector activity in LMC is quite low. However, there has been little work done on exploring just how, and to what extent, these regulations fail. Through the use of stakeholder interviews, this study explored the effectiveness of regulations directed at the private-for-profit sector (general practitioners, private clinics and hospitals) in Zimbabwe. The study found that there was limited and asymmetric knowledge of basic regulations among government bodies and private providers. However, there was a clear feeling that regulations are not being implemented and enforced effectively. A variety of opportunistic practices have been observed among private providers, including: practices of self-referral, where patients are sent to other services the provider has a financial interest in; over-servicing; doctor-patient collusion to collect health insurance payments; and the use of unlicensed staff in private facilities. Key factors limiting effectiveness of regulation in the health sector include the over-centralization and lack of independence of the regulatory body, the absence of legal mechanisms to control the price of care, and the lack of knowledge by patients of their rights. The study also identified a number of potential strategies for improving the current regulatory environment. For example, in order to improve monitoring, 'informal' arrangements between the centralized regulatory body and local authorities developed. There is a need to develop ways to formalize the role of these authorities. In addition, professional associations of private providers are also identified as key players through which to improve the impact of regulation among private providers. Increasing consumer access to information and knowledge is another potential way to improve information within the regulatory process as well as implementation. (+info)
The costs of HIV/AIDS care at government hospitals in Zimbabwe.
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According to official figures, HIV infection in Zimbabwe stood at 700 000-1 000 000 in 1995, representing 7-10% of the population, with even higher expected numbers in 2000. Such high numbers will have far reaching effects on the economy and the health care sector. Information on costs of treatment and care of HIV/AIDS patients in health facilities is necessary in order to have an idea of the likely costs of the increasing number of HIV/AIDS patients. Therefore, the present study estimated the costs per in-patient day as well as per in-patient stay for patients in government health facilities in Zimbabwe with special emphasis on HIV/AIDS patients. Data collection and costing was done in seven hospitals representing various levels of the referral system. The costs per in-patient day and per in-patient stay were estimated through a combination of two methods: bottom-up costing methodology (through an in-patient note review) to identify the direct treatment and diagnostic costs such as medication, laboratory tests and X-rays, and the standard step-down costing methodology to capture all the remaining resources used such as hospital administration, meals, housekeeping, laundry, etc. The findings of the study indicate that hospital care for HIV/AIDS patients was considerably higher than for non-HIV/AIDS patients. In five of the seven hospitals visited, the average costs of an in-patient stay for an HIV/AIDS patient were found to be as much as twice as high as a non-HIV/AIDS patient. This difference could be attributed to higher direct costs per in-patient day (medication, laboratory tests and X-rays) as well as longer average lengths of stay in hospital for HIV/AIDS patients compared with non-infected patients. Therefore, the impact on hospital services of increasing number of HIV/AIDS patients will be enormous. (+info)
Early discharge of infants of low birth weight: a prospective study.
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A total of 495 African infants of low birth weight were discharged from Harari Maternity Hospital, Salisbury, between October 1972 and September 1973. Criteria used for discharge were (a) no clinical evidence of disease, (b) satisfactory feeding by mouth (breast or bottle or both), and (c) stable temperature control under normal room conditions. Of the 495 babies 264 fulfilled these criteria when they weighed 1801-1900 g (group 1), 99 when they weighed 1901-2000 g (group 2), and 132 (group 3) when they weighed 2001-2500 g. The overall follow-up rate of those infants living in greater Salisbury was 85-5%, the health visitor playing an important contributory role in their progress, especially those in group 1. More than two clinic visits in the first four to five weeks after discharge were essential for continuing weight gain in groups 1 and 2 but not in group 3. The mean daily weight gain for all babies at the end of four to five weeks was 26 g. Readmission rates for babies in groups 1,2, and 3 were 9-5%, 1%, and 0-8%, respectively, the largest single cause for readmission being bronchopneumonia associated with hypothermia. Altogether 60% of the readmissions occurred during the two winter months (June and July). Hypothermia, associated with low environmental temperatures played a significant part in morbidity and mortality, and twins, particularly in group 1, had a mortality rate three times greater than singletons in the same group. In general, even in underdeveloped communities singleton babies born outside the winter months with reasonable clinic or home visiting facilities can be discharged at a weight of 1800 g or more. (+info)
Antiquity of the biological sulphur cycle: evidence from sulphur and carbon isotopes in 2700 million-year-old rocks of the Belingwe Belt, Zimbabwe.
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Sulphur and carbon isotopic analyses on small samples of kerogens and sulphide minerals from biogenic and non-biogenic sediments of the 2.7 x 10(9) years(Ga)-old Belingwe Greenstone Belt (Zimbabwe) imply that a complex biological sulphur cycle was in operation. Sulphur isotopic compositions display a wider range of biological fractionation than hitherto reported from the Archaean. Carbon isotopic values in kerogen record fractionations characteristic of rubisco activity methanogenesis and methylotrophy and possibly anoxygenic photosynthesis. Carbon and sulphur isotopic fractionations have been interpreted in terms of metabolic processes in 2.7 Ga prokaryote mat communities, and indicate the operation of a diverse array of metabolic processes. The results are consistent with models of early molecular evolution derived from ribosomal RNA. (+info)