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E Pollak

Publications and source records attributed to E Pollak.

At least 37 records · Page 2Linked to original sources
PubMed1992

Survival probabilities for some multitype branching processes in genetics.

Consider a positively regular, slightly supercritical branching process with K types. An approximation to the probability of survival of a line descended from a single individual of type i has recently been derived by Hoppe. If K is large, however, this approximation may not be easy to compute. A further approximation that is easily computable is given. The result is used to estimate probabilities of survival of an allele A that is originally present in one male or one female in a large, random mating, age-structured population. Both autosomal and sex-linked loci are considered. Another application of the approximation is also discussed.

Alleles↗
PubMed1992

On the theory of partially inbreeding finite populations. III. Fixation probabilities under partial selfing when heterozygotes are intermediate in viability.

In a previous paper by the senior author, an approximation to the probability of survival was given for a mutant, which is originally present in a single heterozygote, in a population that reproduces partly by selfing and partly by random mating. The population was assumed to be very large, but the result obtained is general with regard to the level of dominance in viability. In this paper two errors which were made in that earlier work are corrected. A general approximate expression is then derived for the probability that an allele A is fixed in a partially self fertilizing population of size N, if its initial frequency is p, selection is weak and heterozygotes with the allele are exactly intermediate in viability compared with genotypes AA and AA. A rigorous proof is given for a special case that is a generalization of the classical binomial sampling model. In this case, but not in general, the approximate fixation probability is independent of the probability of reproduction by selfing. Some implications are discussed.

Alleles↗
PubMed1990

The effective population size of an age-structured population with a sex-linked locus.

Let a population have the same age distribution and age-specific sex ratios at times 0, 1, 2,..., and let M, F, and L, respectively, be the numbers of males and females in the youngest age group and the generation interval. It can then be shown that if there is a sex-linked locus the fixation probabilities of a neutral allele are respectively 1/3LM or 1/3LF if the allele first appears in one newborn male or in one newborn female. The effective population size can then be derived. It is the same as for a population with discrete generations having the same means, variances, and covariances of male and female progeny during a lifetime and the same number of individuals entering the population per generation.

Age Factors↗
PubMed1988

On the theory of partially inbreeding finite populations. II. Partial sib mating.

It is assumed that a population has M males in every generation, each of which is permanently mated with c-1 females, and that a proportion beta of matings are between males and their full sisters or half-sisters. Recurrence equations are derived for the inbreeding coefficient of one random individual, coefficients of kinship of random pairs of mates and probabilities of allelic identity when the infinite alleles model holds. If Ft is the inbreeding coefficient at time t and M is large, (1-Ft)/(1-Ft-1)----1-1/(2Ne) as t increases. The effective population number Ne = aM/[1 + (2a-1)FIS], where FIS is the inbreeding coefficient at equilibrium when M is infinite and the constant a depends upon the conditional probabilities of matings between full sibs and the two possible types of half-sibs. When there are M permanent couples, an approximation to the probability that an allele A survives if it is originally present in one AA heterozygote is proportional to FISs1 + (1-FIS)s2, where s1 and s2 are the selective advantages of AA and AA in comparison with AA. The paper concludes with a comparison between the results when there is partial selfing, partial full sib mating (c = 2) and partial sib mating when c is large.

Alleles↗
PubMed1987

On the theory of partially inbreeding finite populations. I. Partial selfing.

Some stochastic theory is developed for monoecious populations of size N in which there are probabilities beta and 1 - beta of reproduction by selfing and by random mating. It is assumed that beta much greater than N-1. Expressions are derived for the inbreeding coefficient of one random individual and the coefficient of kinship of two random separate individuals at time t. The mean and between-lines variance of the fraction of copies of a locus that are identical in two random separate individuals in an equilibrium population are obtained under the assumption that there is an infinite number of possible alleles. It is found that the theory for random mating populations holds if the effective population number is Ne = N'/(1 + FIS), where FIS is the inbreeding coefficient at equilibrium when N is infinite and N' is the reciprocal of the probability that two gametes contributing to random separate adults come from the same parent. When there is a binomial distribution of successful gametes emanating from each adult, N' = N. An approximation to the probability that an allele A survives if it is originally present in one AA heterozygote is found to be 2(N'/N)(FISS1 + (1 - FIS)S2), where S1 and S2 are the selective advantages of AA and AA in comparison with AA. In the last section it is shown that if there is partial full sib mating and binomial offspring distributions Ne = N/(1 + 3FIS).

Alleles↗
PubMed1986

Levels of some organochlorine residues in blood of patients with arteriosclerotic disease.

This study aims to elucidate if any association exists between the development of arteriosclerotic disease and contamination of the internal human environment with certain organochlorine compounds (OCCs). For this purpose the levels of DDT isomers and their metabolites, and of lindane, dieldrin, heptachlor epoxide, and polychlorinated biphenyls (PCBs) were determined in blood serum of 11 patients suffering from slight to moderate (group A), and 24 patients with moderate to severe (group B), arteriosclerotic lesions. The control group consisted of 27 patients with no obvious manifestations of arteriosclerosis. The main findings of the study in comparison with the control group were: Mean OCC residue levels in blood were slightly higher in group A and markedly so in group B; The variability and the extent of departure from normality of distributions of organochlorine insecticides (OCIs) decreased, whereas those of PCBs increased, in arteriosclerotic patients (more markedly in group B); The degree of correlation between blood serum levels of various OCCs was elevated in group A and low in group B. It remains to be ascertained whether changes in the body burden of OCCs are primary, resulting from increased exposure to and absorption of these compounds which thus contribute to the development of arteriosclerosis, or are of secondary origin, due to inhibition of xenobiotic metabolism caused by interference of the arteriosclerotic process with the functions of drug metabolizing enzymes of liver microsomes.

Arteriosclerosis↗
PubMed1986

On three methods for estimating mutation rates indirectly.

Methods for estimating a mutation rate mu has been proposed by Kimura and Ohta; Nei; and Rothman and Adams. It is shown here that all three methods are best applied to rare alleles and that they are all based upon the assumption that all alleles ultimately become extinct. If there is a neutral allele in a growing population, there is conditioning on ultimate extinction, which implies that the underlying stochastic process can be approximated by a branching process for which the mean number of offspring is less than 1. The low numerical values of t0, the mean time to extinction of a line descended from a single mutant, found in two simulation studies, can be attributed to two features. First, the data on which these studies were based came from a fairly rapidly growing population. In such a population, we would expect that extinction, if it does occur, takes place quickly. A second factor is that the effective population size is somewhat lower than the actual number of adults. Population subdivision and migration does not seem to play a significant role. Conservative high and low estimates of mutation rates are computed, and an estimate is obtained for the standard deviation of the estimate of mu. These allow a rough estimate of a 95% confidence interval, which contains estimates of mu found by Neel and Rothman.

Gene Frequency↗
PubMed1985

Rates of sickness absenteeism among employees of a modern hospital: the role of demographic and occupational factors.

Sickness absenteeism, of hospital employees particularly, is a problem of concern due to its negative economic and morale impacts. The aim of the first stage of the study was to identify according to some demographic (sex, age, marital status) and occupational (occupational group, duration of hospital employment) variables those groups of hospital employees who are at higher risk of sickness absenteeism. A comparison with the data of the study performed in the same hospital about 15 years ago showed a rise in the duration of absences with a simultaneous reduction in their incidence. Sickness absenteeism was higher among female, mainly unskilled, workers, presently or previously married, aged from 45 to 60, and employed in the hospital for over ten years. Continuous social and medical surveillance of these employees is suggested as a promising way of reducing sickness absenteeism.

Absenteeism↗