Induction of diploid androgenetic and mitotic gynogenetic Nile tilapia (Oreochromis niloticus L.)

Androgenesis is a potentially valuable technique for recovering fish from gene banks composed of cryopreserved sperm, developing inbred lines, and analyzing patterns of inheritance. The procedure for producing diploid organisms whose nuclear DNA is wholly of paternal origin is dependent on: (1) the denucleation of "host" eggs, and (2) the inhibition of the first mitotic division in order to double the haploid sperm chromosome complement following fertilization of host eggs. Denucleation of tilapia (Oreochromis niloticus L.) eggs was carried out using UV irradiation. Treatment durations of 5-8 rain (total dose of 450-720 J/m 2) produced acceptable yields of viable denucleated eggs [22.9el.6% (eSE) of controls] as estimated by the survival of haploid androgenetic tilapia to 48 h post-fertilization. Successful mitotic inhibition was accomplished using a heat-shock of 42.5~ for 3-4 rain, applied at 2.5-min intervals from 22.5 to 30 min post-fertilization (mpf). The mean survival of androgenetic diploid fish to yolk-sac absorption for treatment groups varied from 0.4% to 5.3%, relative to the controls. Differences in the suceptibility of eggs from different females to UV irradiation were a significant factor in the overall yield of androgenetic diploids. Paternal effects did not significantly influence the androgenetic yield, suggesting that individual males would not be selected against. For comparative purposes mitotic gynogenetic "mitogyne" diploids were produced from UV-irradiated sperm. Mean survival to yolk-sac absorption varied from 0.5% to 10.64%, relative to controls. Similar optima for androgenetic and gynogenetic induction were found in the period 25-27.5 mpf (minutes post-fertilization). Induction treatments would appear to be operating on the same developmental events in both these techniques, and the results suggest that the UV irradiations used do relatively little damage to the eggs beyond nuclear inactivation. The results indicate that the production of androgenetic O. niloticus is possible on a consistent basis and that the application of this technique may be useful in quantitative and conservation genetics

Patient motivations surrounding participation in phase I and phase II clinical trials of cancer chemotherapy

Successful advances in the treatment of advanced malignant diseases rely on recruitment of patients into clinical trials of novel agents. However, there is a genuine concern for the welfare of individual patients. The aim of this study was to examine motives of patients entering early clinical trials of novel cancer therapies. Questionnaire survey with both open- and close-ended questions. The patients were surveyed after they had given informed consent and before or during the first cycle of treatment. In all, 38 phase I/II trial patients participated and completed the survey. Obtaining possible health benefit was listed by 89% as being a 'very important' factor in their decision to participate, with only 17% giving reasons of helping future cancer patients and treatment. Other items cited as a 'very important' motivating factor were 'trust in the doctor' (66%), 'being treated by the latest treatment available' (66%), 'better standard of care and closer follow-up' (61%), and 'closer monitoring of patients in trials' (58%). Only 47% patients indicated that someone had explained to them about any 'reasonable' alternatives to the trial. In total, 71% strongly agreed that 'surviving for as long time as possible was the most important thing (for them)'. Nearly all (97%) indicated that they knew the purpose of the trial and had enough time to consider participation in the trial (100%). In this survey, most patients entering phase I and II clinical trials felt they understood the purpose of the research and had given truly informed consent. Despite this, most patients participated in the hope of therapeutic benefit, although this is known to be a rare outcome in this patient subset. Trialists should be aware, and take account of the expectations that participants place in trial drugs

Resistance to malaria in humans: the impact of strong, recent selection

<p>Abstract</p> <p>Malaria is one of the leading causes of death worldwide and has been suggested as the most potent type of selection in humans in recent millennia. As a result, genes involved in malaria resistance are excellent examples of recent, strong selection. In 1949, Haldane initially suggested that infectious disease could be a strong selective force in human populations. Evidence for the strong selective effect of malaria resistance includes the high frequency of a number of detrimental genetic diseases caused by the pleiotropic effects of these malaria resistance variants, many of which are “loss of function” mutants. Evidence that this selection is recent comes from the genetic dating of the age of a number of these malaria resistant alleles to less than 5,000 years before the present, generally much more recent than other human genetic variants. An approach to estimate selection coefficients from contemporary case–control data is presented. In the situations described here, selection is much greater than 1%, significantly higher than generally observed for other human genetic variation. With these selection coefficients, predictions are generated about the joint change of alleles <it>S</it> and <it>C</it> at the <it>β</it>-globin locus, and for <it>α</it>-thalassaemia haplotypes and <it>S</it>, variants that are unlinked but exhibit epistasis. Population genetics can be used to determine the amount and pattern of selection in the past and predict selection in the future for other malaria resistance variants as they are discovered.</p