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We have estimated genetic variability by gel electrophoresis in three species of krill, genus Euphausia (Arthropoda: Crustacea). Genetic variability is low where trophic resources are most seasonal, and high where trophic resources are most stable. Simlar trends have been found in benthic marine invertebrates. The observed trends of genetic variability do not correlate with trends in the stability of physical environment parameters.
Cultural selection is defined as a modification in gene frequency distributions within a population under the effects of socio-cultural factors. The conditions are examined which determine the efficiency of such a selection mechanism as a driving force for the evolution of the genetic pool of a social group in a state of relative isolation. The possible effect of the cultural variation on the genetic variation of the human species is discussed.
To contribute to the study of the genetic variability of hepatitis C virus (HCV) we have determined the nucleotide sequence of the E2/NS1 and NS3/NS4 regions of a French isolate using the polymerase chain reaction. Comparison of these nucleotide sequences with those available for American and Japanese isolates showed a significant genetic variability: 5 to 33% and 2 to 30% at the nucleic acid and amino acid levels, respectively. The genetic variability is higher in the E2/NS1 (13 to 33% and 12 to 30% at the nucleic acid and amino acid levels, respectively) than in the NS3/NS4 (5 to 21% and 2 to 7%) regions. The sequence of the French isolate is more closely related to that of the American HCV prototype than to the Japanese HCV isolates. This study confirms the extent of HCV genetic variability.
With the increasing maturity of genetic profiling, an essential and routine task in cancer research is to model disease outcomes/phenotypes using genetic variables. Many methods have been successfully developed. However, oftentimes, empirical performance is unsatisfactory because of a "lack of information." In cancer research and clinical practice, a source of information that is broadly available and highly cost-effective comes from pathological images, which are routinely collected for definitive diagnosis and staging. In this article, we consider a Bayesian approach for selecting relevant genetic variables and modeling their relationships with a cancer outcome/phenotype. We propose borrowing information from (manually curated, low-dimensional) pathological imaging features via reinforcing the same selection results for the cancer outcome and imaging features. We further develop a weighting strategy to accommodate the scenario where information borrowing may not be equally effective for all subjects. Computation is carefully examined. Simulations demonstrate competitive performance of the proposed approach. We analyze TCGA (The Cancer Genome Atlas) LUAD (lung adenocarcinoma) data, with overall survival and gene expressions being the outcome and genetic variables, respectively. Findings different from the alternatives and with sound properties are made.
Rapid development of genetic variability may contribute to the pathogenicity of lentiviruses as it may allow escape from immune surveillance and/or from suppression of virus replication. Although apathogenic in African green monkeys, simian immunodeficiency virus isolated from African green monkeys is shown to display extensive genetic variability and defectiveness in the V1- and V2-like variable domains of the external envelope protein comparable to that known for human immunodeficiency virus. However, in contrast to the situation in human immunodeficiency virus-infected individuals, a predominant major virus variant was detected neither in a monkey naturally infected for more than 10 years nor in two monkeys infected with a molecular virus clone for 15-20 months. Extensive variability evolves from a single genotype with a maximal rate of 7.7 mutations per 1000 nucleotides per year. A remarkable selection for nonsynonymous mutations that accounts for 92% of all changes indicates continuous selection of variants.
Inbred strains, outbred strains, and natural populations of rodents differ greatly in the amount and nature of the genetic variability they possess. Consequently, as models of human aging they vary with respect to the areas of research to which they are best suited. Inbred strains, in which all individuals are genetically identical, are best suited as models of specific disease processes and for manipulations involving tissue transplantation. Their lack of genetic variability, however, and the disruption of genetic linkage groups that occurs during inbreeding limit their value as models of more general aging processes. Outbred strains exhibit large interindividual genetic variation--a result of ongoing random accumulation of deleterious alleles with late ages of action. This makes them ideal models for studying the diversity of pathologic lesions, connections between pathologies, and susceptibility to pathologic lesions that collectively produce the reductions in reproductive capacity, physiological efficiency, and viability that are characteristic of aging. Natural populations also may exhibit relatively large amounts of interindividual genetic variability. However, difficulties with husbandry, variable parasite loads, and complex population genetics can compromise their suitability as models of human aging. Ultimately, a consideration of the range of animal models available and a more careful matching of the goals of a study with the genetic system of the model will prove fruitful to gerontology.
The amount of hidden genetic variability within electromorphs in finite populations is studied by using the infinite site model and stepwise mutation model simultaneously. A formula is developed for the bivariate probability generating function for the number of codon differences and the number of electromorph state differences between two randomly chosen cistrons. Using this formula, the distribution as well as the mean and variance of the number of codon differences between two identical or nonidentical electromorphs are studied. The distribution of the number of codon differences between two randomly chosen identical electromorphs is similar to the geometric distribution but more leptokurtic. Studies are also made on the number of codon differences between two electromorphs chosen at random one from each of two populations which have been separated for an arbitrary number of generations. It is shown that the amount of hidden genetic variability is very large if the product of effective population size and mutation rate is large.
A maximum of 22 bands comprising four esterase subgroups--acetylesterase, carboxylesterase, cholinesterase, and acetylcholinesterase--were detected following electrophoresis of lesser snow goose sera on polyacrylamide gels. A minimum of seven structural genes was surmised to be involved in the biosynthesis of these enzymes following physiochemical characterizations. The genetic variability of these loci was calculated to be 1.25% average heterozygosity, while 14.3% of the loci were polymorphic. These estimates of genetic variability were substantially lower than those reported for other vertebrate species. The low degree of genetic variability found in snow goose serum esterases coupled with the extensive protein multiplicity observed may possibly reflect an adaptive strategy based on "biochemical plasticity" rather than genic heterozygosity for this species. The nature of evolutionary forces acting upon multiple enzyme systems such as esterases is discussed. The concept of "conditional neutrality" is introduced and defined within this context.
Genetic background for SHR (SHRSR) and SHRSP and WKY lines were screened by using biochemical genetic markers and class I major histocompatibility complex (RT1) typing. There were many kinds of SHR (SHRSR), SHRSP and WKY inbred lines. The genetic variabilities within SHR (SHRSR) or SHRSP strains were small, but those within WKY strains were not so small. When SHR lines were compared with WKY lines, the allele distribution in SHR lines was different from that in WKY lines at 3-13 loci. Three genetic markers, the Es-3b, Es-4a and PT1k, were identified as specific markers of SHR (SHRSR) and SHRSP. WKY/Izm, WKY/Hos, and WKY/Jim also carried the PT1k as well as SHR lines, but WKY/N and WKY/NCrj had the RT1l haplotype.
A study of cardiovascular risk factors in middle-aged twin men provided an opportunity to test for genetic variability in the SMA 12/60 (Technicon) battery of clinical chemistry tests. Classical twin methodology was used to analyze the variation of monozygotic and dizygotic twins. In addition, frequency of co-twin contact was used to control for effects of differences in shared environment. Genetic variability played a definite role in controlling four of the 11 reported tests: one-hour serum glucose, serum urea nitrogen, uric acid, and bilirubin. No genetic variation was found for lactate dehydrogenase, phosphorus, and alkaline phosphatase. Significantly higher means for calcium, total protein, albumin, and aspartate aminotransferase in monozygotic twins precluded any statement about heredity and environment for these tests.
Mathematical treatments are presented that enable us to compute the amount of genetic variability maintained in a finite population, assuming that mutations occur in stepwise fashion and that both selectively neutral and slightly deleterious alleles are involved. Two numerical examples show that, if very slightly deleterious mutations are prevalent, the amount of genetic variability increases much more slowly as the population number increases than is the case when all the mutations are strictly neutral.
An account is given of the genetic variability in primitive wheats collected from the northwest Pakistan. Apart from genetic sources for disease resistance, drought tolerance, and other plant characters, new sources of possible height reduction in wheat were identified and described. The taller-growing primitive wheats have better emergence, perhaps largely because of their longer coleoptiles. A detailed account is given of comparative genetic studies of height-reducing genes, through both conventional genetic analysis techniques and induced mutation breeding procedures. Both approaches demonstrated the effect of height genes on grain size. At the present time there is a linear relationship between plant height and 1000-kernel weight. Possibilities of achieving a break-through in wheat yields through increased kernel size in short wheats are discussed.
Two African populations of Ceratitis capitata (Kenya and Réunion Isl.) and two Mediterranean ones (Sardinia and Procida Isl.) have been studied for genetic variability at 25 loci by electrophoresis. Wright's FST, Slatkin's Nm* gene flow estimator, Nei's distance (D) together with measures of variability such as H, P, A have been used to compare the population from Kenya with the other three. Parameters using gene frequencies (FST, D, Nm*) indicate the presence of substantial geographic heterogeneity, largely attributable to genetic drift and correlated with dispersion of the medfly from its source area (Subsaharan Africa) to the periphery. The Kenyan population has high genetic variability (assessed by H, P and A), as might be expected given its native status. Significant gene flow estimates between Kenya and the derived Mediterranean populations supports the hypothesis of recent colonization. Part of the geographic heterogeneity is related to the presence of fixed alleles in the more differentiated Réunion population although it maintains the genetic attributes of the ancestral population. Selection or other forces may have played an important role in the differentiation of this population.
Genetic variability among 41 penicillinase non-producing Neisseria gonorrhoeae strains, isolated in Spain, with different levels of resistance to penicillin was investigated by multilocus enzyme electrophoresis. Based on the results obtained by analysis at seven enzyme loci, the strains were separated into 17 electrophoretic types. The average number of alleles/enzyme locus was 2.85; the mean genetic diversity/locus was 0.49 for individual isolates and 0.516 for electrophoretic types. The results showed that these gonococcal strains were, genetically, a highly variable group of organisms.
The quantitative and qualitative distributions of gangliosides were determined in the cerebrum, cerebellum, and brain stem of five inbred strains (C57BL/6J, DBA/2J, LG/J, C3H/HeJ, BALB/cJ) of mice at 21 days of age. Genetic differences were found among the strains for wet weight, absolute amount of gangliosides per region, and concentration of ganglioside (expressed on bolth a wet and a dry weight basis) in all three regions of the brain. The water content of the various brain regions showed the least amount of genetic variability. Coefficients of genetic determination were used to estimate the magnitude of genetic influence on these traits in each brain region. Significant differences were also found among the five strains for the distribution of certain gangliosides. The DBA strain, which is susceptible to audiogenic seizure at this age, had the highest level of the myelin-enriched ganglioside GM1 in all brain regions. Most of the genetic variation that influences the content and distribution of gangliosides among neurologically normal mice can be considered polygenic. Several possible sources of this genetic variation that may contribute to the differences observed among the strains are discussed.
The traditional models of the effect of assortative mating and inbreeding on the genetic variance of polygenic characters (FISHER 1918; WRIGHT 1921) presume that there is no natural selection or mutation. In a large population, the genetic variance determined by additive genes may then increase by up to a factor of two with local inbreeding, and even more with assortative mating. The classical models are still used to interpret data from natural populations. But contrary to their assumptions, most metrical characters in natural populations are usually thought to be under a type of selection which depletes polygenic variation. Mutation is then necessary to maintain genetic variation. The present models show that with the additional features of mutation and selection, in a large population, the mating system has no influence on the amount of genetic variability maintained by additive genes.
The role of genetic variation in isoenzyme gene families is often poorly appreciated. We report here on the determination of DNA sequences and typing of genetic variability in four creatine kinase B (CKB) gene loci in different inbred strains of mice. The unique functional murine CKB gene was found to be nearly identical to the previously characterised rat and human sequences in both size and exon-intron structure. In this gene, approximately 0.5% allelic nucleotide positions as well as the lengths of simple A-rich and [TG]n repetitive elements located at the 5' and 3' sides of the transcribed segment, differed between inbred strains of mice. Preliminary experiments suggest that this sequence divergence is of importance for design of gene targeting strategies involving homologous DNA recombination. The three additional CKB-like gene loci in mice all had the characteristics of processed pseudogenes. By Southern blot analysis we could demonstrate that both the type and number of pseudogenes differed between inbred strains. Analysis of the CKB gene sequences enabled us to speculate about the evolutionary history of this highly polymorphic subfamily of genes.
In North America there are two disjunct forms of grayling, Montana and arctic, which have been separated for approximately 75,000 to 100,000 years. Electrophoretic analysis of thirty-six protein loci in these forms has revealed: (1) levels of gene duplication comparable to other salmonids, (2) a level of heterozygosity similar to other salmonids, (3) a fast and a slow evolving set of proteins, and (4) no obvious relationship between genetic variability and enzyme function. The genetic divergence between these populations may warrant subspecific designations for these two forms.