Statistical Studies on Protein Polymorphism in Natural Populations. III. Distribution of Allele Frequencies and the Number of Alleles per Locus

With the aim of understanding the mechanism of maintenance of protein polymorphism, we have studied the properties of allele frequency distribution and the number of alleles per locus, using gene-frequency data from a wide range of organisms (mammals, birds, reptiles, amphibians, Drosophila and non-Drosophila invertebrates) in which 20 or more loci with at least 100 genes were sampled. The observed distribution of allele frequencies was U-shaped in all of the 138 populations (mostly species or subspecies) examined and generally agreed with the theoretical distribution expected under the mutation-drift hypothesis, though there was a significant excess of rare alleles (gene frequency, 0 ~ 0.05) in about a quarter of the populations. The agreement between the mutation-drift theory and observed data was quite satisfactory for the numbers of polymorphic (gene frequency, 0.05 ~ 0.95) and monomorphic (0.95 ~ 1.0) alleles.—The observed pattern of allele-frequency distribution was incompatible with the prediction from the overdominance hypothesis. The observed correlations of the numbers of rare alleles, polymorphic alleles and monomorphic alleles with heterozygosity were of the order of magnitude that was expected under the mutation-drift hypothesis. Our results did not support the view that intracistronic recombination is an important source of genetic variation. The total number of alleles per locus was positively correlated with molecular weight in most of the species examined, and the magnitude of the correlation was consistent with the theoretical prediction from mutation-drift hypothesis. The correlation between molecular weight and the number of alleles was generally higher than the correlation between molecular weight and heterozygosity, as expected.     

Oestrous and ovarian activity in a female jaguar (Panthera onca).

The mean +/- s.e.m. duration of oestrus was 12.0 +/- 1.0 days (n = 7) and the oestrous cycle length was 47.2 +/- 5.4 days (n = 6) for a captive jaguar. Ovulation did not occur spontaneously, but was induced by treatment with hCG or LH-RH.     

Fine structural abnormalities in the developing mouse embryo

Initial changes in the fine morphology of apparently normal mouse zygotes and embryos were studied in serial sections of mouse oviducts that had been fixed in situ. These changes included extra sperm in the perivitelline space, nuclear budding, the presence of large nucleoli, perinuclear vesicles, the concentration of cytoplasmic organelles, and the extrusion of cytoplasmic ground substance. Initial changes in the nucleus and cytoplasm were undetectable when the zygotes and embryos were examined with the light microscope. It was concluded that serious abnormalities in zygotes and embryos, which may not be identified at the light microscope level, may be detected if they are examined in the electron microscope. Therefore, zygotes and embryos should be critically evaluated before being rated as normal.     

Estimation of time of divergence from phylogenetic studies.

Recent studies with comparative data on base sequences of homologous DNA's or amino acid sequences of homologous proteins indicate that simultaneous estimation of phylogenetic structure and time of divergence is often cumbersome and time consuming. On the other hand, when the topology of an evolutionary tree is known, it is shown in this paper that the least squares theory may be applied to obtain simple estimates of the relative time lengths for each segment of the tree under the assumption of uniform random substitutions in each segment. The method is illustrated with amino acid sequence data on various globin molecules and cytochrome c. The evolutionary significance of some of the estimates is also discussed.     

Genetic structure of the populations migrating from San Luis Potosi and Zacatecas to Nuevo León in Mexico

The Mexicans residing in the Monterrey metropolitan area in Nuevo León, Mexico, were grouped by generation and birthplace [Monterrey Metropolitan Area (MMA), San Luis Potosi (SLP), and Zacatecas (ZAC)] of the four grandparents to determine the extent of genetic variation within this population and the genetic differences, if any, between the natives living in the MMA and the immigrant populations from SLP and ZAC. Nine genetic marker systems were analyzed. The genetic distance analysis indicates that SLP and ZAC are similar to the MMA, irrespective of birthplace and generation. Gene diversity analysis (GST) suggests that more than 96% of the total gene diversity (HT) can be attributed to individual variation within the population. The genetic admixture analysis suggests that the Mexicans of the MMA, SLP, and ZAC, stratified by birthplace and generation, have received a predominantly Spanish contribution (78.5%), followed by a Mexican Indian contribution (21.5%). Similarly, admixture analysis, conducted on the population of Nuevo León and stratified by generation, indicates a substantial contribution from the MMA (64.6%), followed by ZAC (22.1%) and SLP (13.3%). Finally, we demonstrate that there is no nonrandom association of alleles among the genetic marker systems (i.e., no evidence of gametic disequilibrium) despite the Mestizo origin of this population.     

Effects of plant extract Centella asiatica (Linn.) on cold restraint stress ulcer in rats.

Extract of C. asiatica (Linn.) inhibited significantly gastric ulceration induced by cold and restraint stress (CRS) in Charles-Foster rats, Antiulcer activity of plant extract was compared with famotidine (H2-antagonist) and sodium valproate (anti-epileptic). Plant extract, formotidine and sodium valproate showed a dose dependent reduction of gastric ulceration. Plant extract increased brain GABA level which was also dose dependent. Pretreatment with bicuculline methiodide (specific GABAA-antagonist) at the dose level of 0.5 mg/kg im, reversed the antiulcerogenic activity of both plant extract and sodium valproate. Bicuculline as such did not induce gastric ulceration in normal rat.     

Phosphatidylinositol-specific phospholipase C activity as a marker to distinguish between pathogenic and nonpathogenic Listeria species.

In this study, 468 Listeria strains were checked for the presence of phosphatidylinositol-specific phospholipase C (PI-PLC) activity by using a simple assay that consisted of overlaying colonies formed on agar plates with L-alpha-phosphatidylinositol as substrate. In this assay, PI-PLC-active colonies show turbid halos around the colonies as a result of the release of insoluble diacylglycerol from the substrate. This activity was detected only in the pathogenic species Listeria monocytogenes and was not present in any of the 167 strains of Listeria seeligeri, Listeria welshimeri, Listeria innocua, Listeria murrayi, and Listeria grayi tested. Hence, screening for PI-PLC activity permits discrimination between pathogenic and nonpathogenic Listeria species. In particular, the hemolytic but nonpathogenic species L. seeligeri can now be separated from the hemolytic and pathogenic species L. monocytogenes and L. ivanovii. The use of this assay will improve the specific detection and/or isolation of pathogenic Listeria species from clinical samples or food enrichment cultures.     

Base- and sequence-dependent binding of aristololactam beta-D-glucoside to deoxyribonucleic acid

The dependence on base-pair composition and sequence specificity of the (aristololactam beta-D-glucoside)-DNA interaction was examined by spectrophotometric, spectrofluorometric, spectropolarimetric, thermal melting, thermodynamic, and viscometric studies. Binding of this alkaloid to various natural and synthetic DNAs was dependent upon the base composition and sequences of DNA. The binding parameters obtained from spectrophotometric analysis, according to an excluded-site model, indicated a relatively high affinity of the alkaloid binding to GC-rich DNA and alternating GC polymer. This affinity was further evidenced by the quenching of fluorescence intensity, decrease in quantum yield, and perturbations in circular dichroic spectrum. The alkaloid stabilized all DNAs against thermal denaturation. The temperature dependence of the binding constants was used to estimate the thermodynamic parameters involved in the complex formation of the alkaloid with various DNAs. The negative enthalpy and entropy change increased with increasing GC content of DNA and also compensated one another to produce a relatively small Gibbs free energy change. Viscometric studies showed that in the strong binding region the increase of contour length of DNA depended strongly on its base composition and sequence of bases, being larger for GC-rich DNA and alternating GC polymer. On the basis of these observations, it is concluded that the alkaloid binds to DNA by a mechanism of intercalation and exhibits considerable specificity toward alternating GC polymer.     

19F NMR studies on 8-fluoroflavins and 8-fluoro flavoproteins

The 19F NMR spectra of the oxidized and reduced forms of 8-fluororiboflavin, 8-fluoro-FAD, and the 8-fluoroflavin-reconstituted flavoproteins flavodoxin, riboflavin binding protein, D-amino acid oxidase, p-hydroxybenzoate hydroxylase, Old Yellow Enzyme, anthranilate hydroxylase, general acyl-CoA dehydrogenase, glucose oxidase, and L-lactate oxidase were measured. For the proteins studied the oxidized resonances appeared over a 10.1-ppm range, while the reduced resonances were spread over 10.3 ppm. Reduction caused an upfield shift of about 27 ppm for the free 8-fluoroflavins and most of the 8-fluoro flavoproteins. The notable exception was 8-fluoro-FMN flavodoxin, which was shifted 37.6 ppm, indicating an unusually high electron density in the benzene ring. Ligand binding to the oxidized 8-fluoro flavoproteins caused either upfield or downfield shifts of 1.5-5 ppm, depending on the protein/ligand combination. The 8-fluoro-FAD anthranilate hydroxylase resonance was shifted downfield and split into two peaks in the presence of anthranilate. The 8-fluoro-FMN Old Yellow Enzyme resonance was shifted upfield upon complexation with charge-transfer-forming, para-substituted phenolates. The upfield shift increased from less than 1 to 5 ppm as the electron-donating capacity of the phenolate increased. Complexation of native Old Yellow Enzyme with 2,4-difluorophenol caused the fluorine resonances of the ligand to shift and split into two pairs of signals. Each pair of signals was associated with a different isozyme of Old Yellow Enzyme.