RESUMEN
Studying isolation by distance can provide useful demographic information. To analyze isolation by distance from molecular data, one can use some kind of genetic distance or coalescent simulations. Molecular markers can often display technical caveats, such as PCR-based amplification failures (null alleles, allelic dropouts). These problems can alter population parameter inferences that can be extracted from molecular data. In this simulation study, we analyze the behavior of different genetic distances in Island (null hypothesis) and stepping stone models displaying varying neighborhood sizes. Impact of null alleles of increasing frequency is also studied. In stepping stone models without null alleles, the best statistic to detect isolation by distance in most situations is the chord distance DCSE. Nevertheless, for markers with genetic diversities HS<0.4-0.5, all statistics tend to display the same statistical power. Marginal sub-populations behave as smaller neighborhoods. Metapopulations composed of small sub-population numbers thus display smaller neighborhood sizes. When null alleles are introduced, the power of detection of isolation by distance is significantly reduced and DCSE remains the most powerful genetic distance. We also show that the proportion of null allelic states interact with the slope of the regression of FST/(1-FST) as a function of geographic distance. This can have important consequences on inferences that can be made from such data. Nevertheless, Chapuis and Estoup's FreeNA correction for null alleles provides very good results in most situations. We finally use our conclusions for reanalyzing and reinterpreting some published data sets.
Asunto(s)
Variación Genética , Genética de Población/métodos , Modelos Genéticos , Alelos , Animales , Simulación por Computador , Marcadores Genéticos , Repeticiones de MicrosatéliteRESUMEN
Toxoplasma gondii infections can induce serious complications in HIV-infected pregnant women, leading to miscarriage; favour the mother-to-child transmission of HBV and HIV and birth defects. The purposes of this study were: (1) to quantify IgM and IgG antibodies to Toxoplasma gondii in HIV-seropositive and seronegative pregnant women, (2) to identify hepatitis B antigens (HBsAg) in pregnant women and (3) to determine T. gondii and HBV co-infections among these patients. The study was conducted at Centre Medical Saint Camille, in Burkina Faso from January to June 2009. A total of 276 HIV-infected and uninfected pregnant women were included. All women had less than 32 weeks of amenorrhoea and were aged from 19 to 42 years. Toxoplasma gondii antibodies and HBsAg were detected using ELISA method. In addition, women freely agreed to answer a questionnaire. The results of our investigations revealed that, among these pregnant women, 38.8% were illiterates, 50.4% were housewives and only 5.4% were civil servants. Positive T. gondii-specific IgM (4.7%) and IgG (27.2%) were detected. In this study, we found that HIV-seropositive status seem to be associated with great prevalence rates of both T. gondii (31.9 vs. 22.5%) and HBV (13.0 vs. 5.8%). The elevated co-infection rate in HIV-positive women suggested that they are exposed to T. gondii and HBV infections prevalently because of their immune depression. Therefore, to reduce the prevalence of T. gondii and HBV among HIV-seropositive pregnant women, lamivudine could be included in their HEART and women should follow healthy lifestyle formation.