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Biomedical subjects

R C Lewontin

Publications and source records attributed to R C Lewontin.

At least 55 records · Page 3Linked to original sources
PubMed1975

Selection in complex genetic systems III. An effect of allele multiplicity with two loci.

A two-locus model with three alleles at one locus and two at the other is studied. The viability system is such that all double heterozygotes have fitness unity, all single heterozygotes have fitness w smaller than 1 and all double homozygotes have fitness w-2. The following are the major findings: 1. There are more stable equilibria for tight linkage than in the corresponding three-locus model, even though the number of chromosomes is lower. 2. The equilibria stable for tight linkage do not belong to a unique high complementarity class, as is the case for two alleles at each locus. Instead the strength of selection determines the structure of the equilibrium. 3. The increase in number of alleles seems to reduce the possible extent of association between the loci. 4. The measure of this association is not well defined, although we have suggested a statistically standard way of getting over this. 5. A mutation introduced while a population is in linkage disequilibrium may, per medium only of the change in number of alleles, destroy the linkage disequilibrium.

Alleles↗
PubMed1974

Molecular heterosis for heat-sensitive enzyme alleles.

Heat denaturation studies were carried out and revealed hidden genic variants with the same net charge at the Octanol dehydrogenase-1 locus in Drosophila pseudoobscura. Studies of several genetic crosses between strains with different heat-sensitivity alleles showed that the F(1) retained more in vitro enzyme activity after being heat-treated for a specified amount of time at a given temperature than the heat-resistant parent. We call this phenomenon "heterosis for heat-stability of enzyme activity" and discuss its possible molecular mechanism, its relation to maintenance of genetic variation in natural populations, and its bearing on the "classical" and "balance" hypotheses.

Alcohol Oxidoreductases↗
PubMed1973

Distribution of gene frequency as a test of the theory of the selective neutrality of polymorphisms.

The variation in gene frequency among populations or between generations within a population is a result of breeding structure and selection. But breeding structure should affect all loci and alleles in the same way. If there is significant heterogeneity between loci in their apparent inbreeding coefficients F=s(p) (2)/p(1-p), this heterogeneity may be taken as evidence for selection. We have given the statistical properties of F and shown how tests of heterogeneity can be made. Using data from human populations we have shown highly significant heterogeneity in F values for human polymorphic genes over the world, thus demonstrating that a significant fraction of human polymorphisms owe their current gene frequencies to the action of natural selection. We have also applied the method to temporal variation within a population for data on Dacus oleae and have found no significant evidence of selection.

Gene Frequency↗
PubMed1973

Population genetics.

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Alcohol Oxidoreductases↗
PubMed1971

The effect of genetic linkage on the mean fitness of a population.

If many gene loci are kept in a segregating state by natural selection, the equilibrium frequencies of the genotypes in the population may be a function of the amount of recombination among the genes. It is shown that if the equilibrium vector of gametic frequencies is a continuous function of the set of recombination frequencies among genes, then the mean fitness of the population at equilibrium is a maximum in the absence of recombination. Thus, in general, restriction of recombination increases fitness.

Gene Frequency↗
PubMed1969

On population growth in a randomly varying environment.

If a population is growing in a randomly varying environment, such that the finite rate of increase per generation is a random variable with no serial autocorrelation, the logarithm of population size at any time t is normally distributed. Even though the expectation of population size may grow infinitely large with time, the probability of extinction may approach unity, owing to the difference between the geometric and arithmetic mean growth rates.

Ecology↗