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PubMedDate not supplied

Familial aggregation in the presence of temporal trends.

Models for assessing temporal trends in familial aggregation are described for both cross-sectional and longitudinal family data. Simultaneous linear structural equations on latent variables are used to model the dependence among family members. The coefficients of the equations are assumed to be parametric functions of time, so that quite complex temporal trends in familial aggregations can be accommodated. Variable family sizes and missing data values pose no problem as the parameters of the models are estimated via maximum likelihood techniques. One of the models is applied to systolic blood pressure data in 542 Japanese-American nuclear families. The results indicate limited evidence for temporal variation in the genetic expression, but that there is substantial temporal variation in environmental influences, which appear to peak at middle age.

Age Factors↗
PubMed2001

Investigation of novel polymorphisms within the 3' region of the IL-6 gene in patients with rheumatoid arthritis using Genescan analysis.

A highly polymorphic AT rich repeat exists in the 3' flanking region of the IL-6 gene. Using Genescan analysis we studied this region of the IL-6 gene in 55 normals and 95 patients with rheumatoid arthritis (RA). The influence of alleles on need for early major joint surgery in RA patients was assessed. We identified nine alleles of which, G8, G7 and G4 were the most common (37% vs 36% vs 13%). RA surgery patients had an increase in the frequency of G7 compared to non-surgery and control populations (46% vs 27% vs 34%, respectively) and a decrease in G8 (22% vs 46% vs 43%, respectively). RA patients homozygous for G8 had a lower ESR than those homozygous for G7 (23 mm/h vs 36 mm/h) although this was not significant. We have determined these alleles and their distribution in a normal and RA population. Initial findings suggest G8 may be associated with lower erythrocyte sedimentation rate (ESR) and less severe RA. Although trends in allele distribution were observed, further studies in larger cohorts are required.

Alleles↗
PubMed1995

Relative efficiencies of chi 2 models of recombination for exclusion mapping and gene ordering.

In multilocus linkage analysis, it is common to assume chiasma interference is absent. While this assumption provides mathematical tractability, there is substantial biological evidence contradicting it, particularly when the loci are closely spaced. The chi 2 class of recombination models, recently described by Foss et al. (Genetics 133: 681-691, 1993), has a plausible biological basis and provides a dramatically improved fit over virtually all other models currently in use. Here, a simulation study is performed to assess the relative efficiency of a no interference model analysis to an analysis with a chi 2 model which allows for interference. The results presented show that analysis with the no interference model is inefficient in the presence of interference.

Chi-Square Distribution↗
PubMed1994

A graphic approach to analyzing codon usage in 1562 Escherichia coli protein coding sequences.

The occurrence frequencies of the four bases (adenine, cytosine, guanine and thymine) at each of the three codon positions for 1562 Escherichia coli protein coding sequences have been calculated. The 1562 x 4 x 3 = 18,744 data thus obtained have been analyzed by a graphic method in which the four base occurrence frequencies at each codon position for each coding sequence are represented by a point in a three-dimensional space. Thus, the 18,744 data, which would otherwise occupy several printed pages, can be intuitively displayed by a graphy. The point distribution pattern for each of the three codon positions has been analyzed. The results of our analysis indicate that the patterns for the first two codon positions reflect the origin for producing native folding structures of proteins. We thus come to the conclusion that the distribution patterns for the first two codon positions should be basically species-independent, as confirmed by studies for a number of other species. However, the distribution pattern for the third codon position is species-dependent. Based on the point distribution of the third codon position, six collective parameters have been defined to describe the overall feature of the pattern concerned. These collective parameters can be generally used to classify different species, and hence would be a useful vehicle for studies in taxonomy. In addition to E. coli, the collective parameters for a number of other species have been calculated and analyzed.

Animals↗
PubMed1995

The maximum information principle and the evolution of nucleotide sequences.

The probability distributions of bases in nucleotide sequences are deduced from the maximum information principle by maximizing the entropy (due to random mutation of bases) under certain constraints (Markovian entropy, G + C content, etc, due to selection). Two formulations are given with respect to different selective constraints. The deviations of theoretical distributions from experimental data are lower than 10% for most sequences. It is shown that the Lagrange multipliers change from species to species systematically--i.e. selective constraints correlate with evolution.

Animals↗
PubMed2001

Estimating nucleotide diversity from random amplified polymorphic DNA and amplified fragment length polymorphism data.

A way to estimate the index of nucleotide diversity (pi) from band match frequencies in random amplified polymorphic DNA and amplified fragment length polymorphism data is described. pi is shown to be a simple function of the proportion of mismatched bands between two individuals drawn at random from a population (phi) and the number of discriminating sites in the amplification system. The method is computationally and conceptually simple and avoids some of the assumptions inherent in other approaches: the relationship is independent of the base composition of the target DNA and avoids the bias inherent in estimations of allelic frequencies in dominant systems. Only two individuals from a population are needed to estimate pi. This economy of material suggests utility of this approach in conservation genetics or other fields where obtaining large samples is impractical or undesirable.

Alleles↗
PubMed2000

Most recent common ancestor probability distributions in gene genealogies under selection.

A computational study is made of the conditional probability distribution for the allelic type of the most recent common ancestor in genealogies of samples of n genes drawn from a population under selection, given the initial sample configuration. Comparisons with the corresponding unconditional cases are presented. Such unconditional distributions differ from samples drawn from the unique stationary distribution of population allelic frequencies, known as Wright's formula, and are quantified. Biallelic haploid and diploid models are considered. A simplified structure for the ancestral selection graph of S. M. Krone and C. Neuhauser (1997, Theor. Popul. Biol. 51, 210-237) is enhanced further, reducing the effective branching rate in the graph. This improves efficiency of such a nonneutral analogue of the coalescent for use with computational likelihood-inference techniques.

Algorithms↗
PubMed2001

Competition at the mouse t complex: rare alleles are inherently favored.

We investigate the competition between alleles at a segregation distorter locus. The focus is on the invasion prospects of rare mutant distorter alleles in a population in which a wildtype and a resident distorter allele are present. The parameters are chosen to reflect the situation at the t complex of the house mouse, one of the best-studied examples of segregation distortion. By analyzing the invasion chances of rare alleles, we provide an analytical justification of earlier simulation results. We show that a new distorter allele can successfully invade even if it is inferior both at the gamete and at the individual level. In fact, newly arising distorter alleles have an inherent rareness advantage if their negative fitness consequences are restricted to homozygous condition. Likewise, rare mutant wildtype alleles may often invade even if their viability or fertility is reduced. As a consequence, the competition between alleles at a segregation distorter locus should lead to a high degree of polymorphism. We discuss the implications of this conclusion for the t complex of the house mouse and for the evolutionary stability of "honest" Mendelian segregation.

Alleles↗
PubMed1988

The maintenance of transposable elements in natural populations.

Models of the maintenance of transposable elements in randomly mating host populations are reviewed. It is shown that the data on the distribution of copy numbers between individuals are largely concordant with what is expected on the basis of the Mendelian transmission of elements. The role of regulation of rates of transposition, and of various modes of natural selection, in maintaining an equilibrium in copy numbers in the face of transpositional increase in copy number is discussed. Tests for the role of selection against insertional mutations and against chromosome rearrangements induced by exchange between homologous elements located at nonhomologous chromosome locations are discussed. Reasons for expecting elements to accumulate in chromosome regions where crossing over is restricted are discussed, and data suggesting the existence of such an effect are described. Theory and data on the probability distribution of element frequencies at individual chromosomal sites are described. It is concluded that the available population data are consistent with the notion that element abundances are largely controlled by the interaction of transpositional increase in copy number with opposing forces.

Animals↗
PubMed2004

Methyltetrahydrofolate reductase polymorphism influences onset of Huntington's disease.

Onset of Huntington's disease (HD) negatively correlates with CAG repeat length of the HD gene, which encodes the protein huntingtin. This protein interacts with the homocysteine metabolizing enzyme cystathionine betasynthase (CBS). Objective of this study was to analyze the impact of CAG repeats, polymorphisms of various homocysteine metabolizing enzymes, like CBS, Methyltetrahydrofolate Reductase (MTHTR), Methionine Synthase Reductase (MSR) and methionine synthase (MS) on HD onset in 171 patients. The significant impact of CAG repeats on HD onset (chi2= 25.54, FG = 4, p<0.0001) with a significant correlation between both (R= -0.521, p=0.01) was obvious. HD patients with the homozygous MTHFR-1298-CC significantly (p = 0.024) earlier experienced HD symptoms. There was no influence demonstrable of CBS, MSR and MS. Determination of MTHFR polymorphisms and CAG repeats enables screening for subjects with putative early HD onset in order to study neuroprotective compounds in their efficacy to delay HD symptoms.

Adult↗
PubMed1990

Segregation analysis of 1885 DMD families: significant departure from the expected proportion of sporadic cases.

The proportion of sporadic cases of Duchenne muscular dystrophy has been estimated by classical segregation analysis in a pooled sample of 1885 sibships from 7 different countries. A significant departure from the theoretical expectations based on mutation-selection equilibrium is observed (segregation frequency = 0.439 +/- 0.017; frequency of sporadic cases = 0.229 +/- 0.026, at the maximum likelihood). The occurrence of germinal mosaicism in some of the mothers of Duchenne cases may account for this peculiar finding, although a possible role of inequality of mutation rates in the two sexes cannot be ruled out.

Chromosomes, Human↗
PubMed1976

Possible genetic consequences of relaxed selection against common disorders with complex inheritance.

With increasing success in medical treatment for many common disorders with complex inheritance, it is expected that the incidence of patients requiring treatment will gradually rise from generation to generation. While this is theoretically true for a long range of future, the pattern of possible increase in the frequency of a disorder resulting from complete cure has been examined with special reference to the next few generations. It was shown that the maximum possible increment will take place in the first generation, with additional increment rapidly diminishing with subsequent generations. For congenital heart disease, for example, the restoration of full fertility to all of the patients would incur an increase in the frequency at birth of the disease by about 10% after 5 to 10 generations.

Forecasting↗