No place like home: competition, dispersal and complex adaptation.

In many groups of organisms the location of settling is determined by competition, and fitter individuals tend to settle closer to their natal territory than less fit ones. In this work we study the implications of this phenomenon to the problem of adaptation and speciation on a rugged adaptive landscape. One consequence of fitness-associated dispersal (FAD) is that individuals with high fitness are more likely to experience inbreeding, especially with other fit individuals. Another consequence is that when dispersal is costly, the less fit individuals are more likely to pay the cost. When a rare and advantageous allelic combination appears, FAD may increase its chances to spread in the population. In a two-locus two-alleles model with negative epistasis, we find that FAD significantly shortens the waiting time for an adaptive peak shift in comparison with random dispersal.

Allele frequencies of nine STR loci of Jewish and Arab populations in Israel.

DNA typing of nine short tandem repeat (STR) loci was carried out on unrelated Israeli Jewish and Arab individuals. All loci were highly polymorphic and the distribution of the obtained genotypes did not deviate from Hardy-Weinberg equilibrium. A comparison between Jewish and Arab population data revealed statistically significant differences in allele frequency distributions for some of the loci. The results presented in this study enable the use of these nine STR loci for forensic, identification and paternity cases in the Jewish and the Arab populations of Israel.

Genetic variation of three tetrameric tandem repeats in four distinct Israeli ethnic groups.

The allele frequency distributions of three STR loci amplified by PCR have been studied in four Israeli communities: Ashkenazi Jews and three non-Ashkenazi groups, namely Moroccan, Yemenite, and Ethiopian Jews. The loci analyzed were CSF1PO, TPOX, and HUMTHO1. The typing was performed in sequencing polyacrylamide gels under denaturing conditions that could separate alleles with differences of a single base. The population data were analyzed with respect to Hardy-Weinberg (H-W) equilibrium and found that all loci meet the H-W expectations. No-ticeable differences were encountered between the four Jewish ethnic groups studied hereby indicating the importance of establishing a local database to be used in human identity testing in these different Israeli Jewish groups.

Chorionic villus sampling prior to pregnancy termination, a tool for forensic paternity testing.

Chorionic villus sampling (CVS), prior to pregnancy termination (pre-termination CVS), is suggested as a tool for forensic paternity testing. Unlike the abortion material, which consists of ruptured tissues of fetal and maternal origin, extra-embryonic membranes obtained through CVS can provide an uncontaminated source of fetal tissue for genotyping. We discuss the possibility of confined placental mosaicism (CPM) and its implications on the polymerase chain reaction (PCR) based analyses of short tandem repeats (STRs) and the D1S80 loci.

Molecular analysis of HLA class II polymorphisms among different ethnic groups in Israel.

The Jewish population in Israel comprises of inhabitants of heterogeneous ethnic backgrounds. Genetic studies classify the Israeli Jewish population into two major groups: Ashkenazi from Central and Eastern Europe and Sephardic or non Ashkenazi, from the Mediterranean and North Africa. The present study was aimed at elucidating the differential influx of HLA class II alleles in Ashkenazi, in various non-Ashkenazi subgroups and in Israeli Moslem Arabs. Using the PCR-SSOP technique, a large number of alleles were detected at each of the loci examined (DRB1, DQA1 and DQB1). In addition, gene frequencies, characteristic DR/DQ linkage disequilibria, population distance and their corresponding dendogram, were used to study the relationship between Israelis as a group, non Jewish Caucasians and Blacks. These populations could be grouped into three main clusters: the first consists of all the Israeli groups with the exception of the Ethiopian Jews; the second consists of non Jewish Caucasians, with a clear distinction seen between Israelis and non Jewish Europeans and U.S. Caucasians; the third, composed of Blacks, is distinctly different from the other populations. Ethiopian Jews were found to be closer to the Blacks than to any of the Israeli Jewish groups. We have shown that Jews share common features, a fact that points to a common ancestry. A certain degree of admixture with their pre-immigration neighbors exists despite the cultural and religious constraints against intermarriage.

Forensic identification of a rapist using unusual evidence.

This case report demonstrates a rape case, where no semen, hair, or fingerprints were left by the perpetrator at the crime scene, but rather uncharacteristic biological and physical evidence in the form of a lollipop and a pair of glasses. Three separate forensic laboratories collaborated using conventional forensic methods of PCR DNA typing, photography, and toolmark comparisons to provide investigators with scientific evidence which in turn was instrumental in bringing a violent criminal to justice. The importance of evaluating each item of evidence and realizing its forensic value is stressed in this case report.

Continuous stability and evolutionary convergence.

A stochastic process of long-term evolution due to mutation and selection is defined over an asexually reproducing population, with selection according to a population game with a one-dimensional continuity of pure strategies. Limiting the analysis to mutations of small effect, it is shown that long-term dynamic stability in such a process is equivalent to continuous stability in the relevant population game. In the case of a one-dimensional strategy set (but not necessarily if the strategy set is multi-dimensional), this result is virtually independent of the distribution of mutations.

Affected sib pair identity by state analyses.

Four methods using identity by state (IBS) data from affected sib pairs are compared for their ability to detect linkage between a diallelic marker and disease. A joint null hypothesis of no linkage and no linkage disequilibrium between the marker and disease must be considered. Two tests have undesirable properties in the case of linkage disequilibrium. Which of the other two tests has more power is dependent on the presence or not of linkage disequilibrium. The procedure of choice when possible is to type parents of affected sib pairs: the null hypothesis of no linkage can then be tested using identity by descent (IBD) values from informative parents, and the null hypothesis of no marker association with disease (linkage equilibrium) can be tested independently using the marker allele frequencies in the affected sib pairs.

The differences among Jewish communities--maternal and paternal contributions.

The haplotypes of Y chromosome (paternally inherited) and mtDNA (maternally inherited) were analyzed in representatives of six Jewish communities (Ashkenazic, North African, Near Eastern, Yemenite, Minor Asian/Balkanian, and Ethiopian). For both elements, the Ethiopian community has a mixture of typically African and typically Caucasian haplotypes and is significantly different from all others. The other communities, whose haplotypes are mostly Caucasian, are more closely related; significant differences that were found among some of them possibly indicate the effects of admixture with neighboring communities of non-Jews. The different contribution of the Y chromosome and mtDNA haplotypes to the significant differences among the communities can be explained by unequal involvement of males and females in the different admixtures. In all communities, except the Ethiopians, the level of diversity (h) for Y chromosome haplotypes is higher than that for mtDNA haplotypes, suggesting that in each community the people who become parents include more males than females. An opposite proportion (more females than males) is found among the Ethiopians.

Sequential sampling in determining linkage between marker loci and quantitative trait loci.

As compared to classical, fixed sample size techniques, simulation studies showed that a proposed sequential sampling procedure can provide a substantial decrease (up to 50%, in some cases) in the mean sample size required for the detection of linkage between marker loci and quantitative trait loci. Sequential sampling with truncation set at the required sample size for the non-sequential test, produced a modest further decrease in mean sample size, accompanied by a modest increase in error probabilities. Sequential sampling with observations taken in groups produced a noticeable increase in mean sample size, with a considerable decrease in error probabilities, as compared to straightforward sequential sampling. It is concluded that sequential sampling has a particularly useful application to experiments aimed at investigating the genetics of differences between lines or strains that differ in some single outstanding trait.

Co-operation and defection: playing the field and the ESS.

If food is patchily dispersed, food clumps being very rich, but rare and hard to find, each individual in a foraging flock then faces an evident dilemma: whether to co-operate and participate in the search, thus enhancing the rate by which rich patches are discovered, or to defect and let others do the searching, thus avoiding any possible expenditures and risks involved in the search (but enjoying the abundant resources once a rich patch is discovered). This conflict (and its possible solution) is treated as an example in the analysis of the synergistic n-player game presented in this paper. After deriving conditions for the existence of a mixed ESS in such games, the evolutionary stability of the mixed strategy against invasions by pure strategists, in particular against invasions by recognizable defectors, is analyzed. Whereas in any "degenerating" mixed-strategy model a recognizable defector can invade and spread, a "non-degenerating" model can sometimes yield a mixed ESS which is immune to such invasions.

Affected kin-pair IBD methods: genetic models.

Cases of interest using affected sib-pair methods to distinguish between recessive and additive (dominant) modes of inheritance of a disease-predisposing gene involve goodness-of-fit tests with a small expected number in the "share-zero parental haplotypes" category, as well as an unknown parameter, the frequency of the disease-predisposing allele. Our simulations demonstrate that the real significance level of the chi-square test using the three-haplotype-sharing IBD values (share 2, 1, and 0 parental haplotypes) is close to the assumed (.05) level in these cases, so that the haplotype-sharing classes do not have to be lumped, which would leave no degrees of freedom for a statistical test. The validity of the chi-square approximation in cases of small expected frequencies has previously been described, but the situations that have been considered do not cover the very small values in the share-zero category that are often expected in the affected sib-pair analysis, nor do they involve estimation of an unknown parameter. Although including IBD values from affected kin pairs other than sibs can be a very powerful tool in demonstrating linkage of a marker and disease, these pairs do not add power, in fact they reduce the power, of the chi-square tests of goodness-of-fit of modes of inheritance.

Should a parasite expose itself? (some theoretical aspects of begging and vigilance behavior).

This paper examines the evolutionarily stable (ESS) solution of the begging conflict in cases involving nest parasitization. As expected, the presence in the nest of a parasite chick leads to a more intense begging conflict, with the parasite displaying a more selfish behavior than the host chicks. The model also predicts opposite responses by the host and the parasite to changes in the number of nestmates. While a larger number of nestmates entails a reduced ESS begging intensity for each of the host chicks, it entails an increased begging intensity for the parasite. Consequences of the parasite's ability to disguise itself are compared to analogous results for the vigilance game: whereas in the begging game a parasite should conceal itself, exposure can be selectively advantageous for a defector in the vigilance game.

Evolutionarily stable strategies of mutual help between relatives having unequal fertilities.

The evolutionarily stable strategy of mutual help between relatives having unequal fertilities is studied in a kin selection model, which also takes into account competition between kins and the possibility of reciprocation. It turns out that competition and reciprocation can establish ESSs which are completely different from those expected by Hamilton's basic theory.

The affected sib method. IV. Sib trios.

The classical sib pair method uses the expected and observed HLA (human leukocyte antigen) haplotype sharing distribution in sib pairs, who are affected with an HLA associated disease, to make inferences about the inheritance of the disease. In this paper we present the expected HLA haplotype sharing distributions in affected sib trios, and sib pairs, from families with three or more affected sibs. The underlying model for both distributions, as for the classical sib pair method, is that disease predisposition is determined by a single allele at an HLA-linked locus. The sib trio tests of hypotheses (additive and recessive), and disease parameter estimates (additive, recessive and intermediate), can be compared with those obtained from the classical sib pair analysis. In addition, the sib trio data allow parameter estimation for a general disease model to be made, if the data fall within the bounds of the expectation. This study forms the basis of later investigations which show that haplotype sharing of affected sib trios for two susceptibility alleles (negative complementation) model, which appears appropriate for insulin dependent diabetes mellitus (IDDM), moves outside the bound of the single susceptibility expectations outlined here, whereas haplotype sharing values for sib pairs are bound by the single susceptibility allele expectations. Available Caucasian IDDM data have been analysed. The results support genetic heterogeneity of IDDM.

The affected sib method. I. Statistical features of the affected sib-pair method.

The distribution of the number of HLA haplotypes shared by sibs affected with the same HLA-linked disease can be used to obtain information on the genetics of the disease. Since the inception of the use of sib-pair methods for the analysis of the HLA-associated diseases, the question has been raised of how to include families with more than two affected sibs in the sib-pair analysis. This paper presents appropriate weighting schemes. A procedure for estimating the frequency of the disease allele in the general population, under the assumptions of single-allele recessive, additive, dominant and intermediate models, with negligible recombination (theta = 0) between the disease-predisposing gene and the HLA region, and no selective disadvantage of the trait, is also given. Cluster-sampling techniques are used in the analysis.

Statistical aspects of measuring the strength of associations between HLA antigens and diseases.

It will be demonstrated that the delta measure (attributable risk) of Bengtsson & Thomson (1982) can be used in a wide variety of cases to determine which of a number of HLA antigens associated with a particular disease allele has the strongest genetic association. Tests of significance and confidence intervals for the delta measure will be discussed.