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PubMed1994

Linkage disequilibrium in growing and stable populations.

Nonrandom associations between alleles at different loci can be tested for using Fisher's exact test. Extensive simulations show that there is a substantial probability of obtaining significant nonrandom associations between closely or completely linked polymorphic neutral loci in a population of constant size at equilibrium under mutation and genetic drift. In a rapidly growing population, however, there will be little chance of finding significant nonrandom associations even between completely linked loci if the growth has been sufficiently rapid. This result is illustrated by the analysis of mitochondrial DNA sequence data from humans. In comparing all pairs of informative sites, fewer than 5% of the pairs show significant disequilibrium in Sardinians, which have apparently undergone rapid population growth, while 20% to 30% in !Kung and Pygmies, which apparently have not undergone rapid growth, show significance. The extent of linkage disequilibrium in a population is closely related to the gene genealogies of the loci examined, with "star-like" genealogies making significant linkage disequilibrium unlikely.

Alleles↗
PubMed2004

Occurrence in the field of a long-term, year-round, stable population of placozoans.

Long-term field studies on placozoans (Trichoplax adhaerens), including both substrate sampling and slide sampling, were carried out at a subtidal site near Shirahama, Japan. Samples of natural substrate materials from the field, such as stones, shells, or fragments of coral, were particularly useful for obtaining placozoans. Results from the substrate sampling indicate that placozoans are present year-round at the study site. Large intermittent peaks in the number of animals collected at the study site occurred roughly once a year, between late summer and the beginning of winter. Placozoans were present every year from 1989 through 2000. A seawater aquarium was also studied and provided a considerable number of placozoans for more than 1 year.

Animals↗
PubMed2002

Incidence of symptomatic thrombosis in a stable population of 650,000: travel and other risk factors.

Despite recent intensive media interest, the incidence of traveler's thrombosis is unknown. We have undertaken a study of all symptomatic cases of venous thrombosis, presenting to a hospital, in a fixed population of 650,000. There were 1,250 cases of venous thromboembolism diagnosed over a 2-yr period. Of these, only 47 (3.8%) answered positively to the question" did you make a journey of more than 100 mi in the 4 wk prior to diagnosis?" Among the travelers, 60% had traveled by air, 36% by road, and the remainder by rail. At least one medical risk factor for venous thrombosis was present in all but three of our cohort. We conclude that, taking into consideration the enormous number of passengers who travel, the relative risk of traveler's thrombosis is likely to be low. The incidence of this complication in the North East of England is 1 per 27,660 of the whole population.

Acute Disease↗
PubMed1997

Brazil: model life tables and stable population.

"In the 1974 Meeting of the Brazilian Association for Population Studies, Frias and Leite presented a set of model life tables that were meant to reflect the sex-age structure of Brazilian mortality. A later examination of this study revealed the need for revision and further development in order to improve this valid piece of work." The present article reviews and complements the earlier study.

Age Distribution↗
PubMed1983

Generalization of the immigration and the stable population model.

Building upon an idea presented by Espenshade, Bouvier and Arthur (1982) about the eventual stationarity of a population subjected to a net reproduction rate of less than one and a constant stream of immigration, this note reports the consequences upon the birth trajectory for all possible values of the net reproduction rate. It has been shown that when the net reproduction rate is equal to one, the number of births increases linearly with time. As may be expected, the increase is exponential for values of net reproduction rate greater than one.

Emigration and Immigration↗
PubMed1996

Population genetics and gene variation of stable fly populations (Diptera:Muscidae) in Nebraska.

Genetic variation in stable fly, Stomoxys calcitrans (L.), populations from Nebraska, Canada, and Texas was sampled. Four of 12 allozyme loci were polymorphic, with an average of 1.7 alleles per locus. Observed and expected heterozygosities were 0.086 and 0.070, respectively. Nei's genetic distance between populations averaged 0.001 and ranged from 0.000 to 0.005. Wright's F statistics revealed greater variation within than among populations. Allele frequencies were homogeneous among temporal samples from a single population. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of 6.4 kb of the mitochondrial DNA genome with 16 restriction enzymes revealed no variation in stable fly populations from Canada, Nebraska, and Texas. PCR-RFLP analysis of a 2.0-kb fragment of the nuclear ribosomal DNA internally transcribed spacer region also revealed no variation. The lack of genetic differentiation among stable fly populations indicates high levels of gene flow among populations. The low levels of variation observed with biochemical and molecular techniques are consistent with a genetic bottleneck during stable fly colonization of North America.

Animals↗