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J F Crow

Publications and source records attributed to J F Crow.

At least 19 recordsLinked to original sources
PubMed1991

Was Wright right?

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Biological Evolution↗
PubMed1991

Haploidy or diploidy: which is better?

Although the evolutionary advantages of sexual reproduction have been extensively discussed, much less attention has been paid to haploid and diploid phases of the sexual life cycle. The relative lengths of these phases differ greatly in various taxa, including as extremes those with one or the other phase reduced to a single cell. Here we consider the efficiency of elimination of deleterious mutations as an evolutionary force and compare the mutation loads under haploid and diploid selection, Ln and L2n. With truncation-like selection, partial dominance, and heterozygous effect of a mutation less than about 1/4 its hemizygous effect, L2n less than Ln; otherwise L2n greater than Ln. The difference becomes important when the genomic deleterious mutation rate exceeds about 1 per genome. This suggests that the mutation rate, degree of dominance and mode of selection can be important in life-cycle evolution.

Biological Evolution↗
PubMed1991

Why is Mendelian segregation so exact?

The precise 1:1 segregation of Mendelian heredity is ordinarily taken for granted, yet there are numerous examples of 'cheating' genes that perpetuate themselves in the population by biasing the Mendelian process in their favor. One example is the Segregation Distortion system of Drosophila melanogaster, in which the distorting gene causes its homologous chromosome to produce a nonfunctional sperm. This system depends on three closely linked components, whose molecular basis is beginning to be understood. The system is characterized by numerous modifiers changing the degree of distortion. Mathematical theory shows that unlinked modifiers that change the degree of distortion in the direction of Mendelism always increase in the population. This provides a mechanism for removing cheaters and preserving the honesty of the Mendelian gene-shuffle.

Alleles↗
PubMed1990

Alternative fitness models with the same allele frequency dynamics.

For any set of one- or two-locus genotypic fitnesses there are alternative sets, usually frequency-dependent and often with quite different biological meanings, that give rise to the same equations for change of allele or haplotype frequencies. Therefore, it is not possible to distinguish among alternative fitness models from allele or haplotype frequency trajectories or equilibrium distributions. For a single locus and for two loci when linkage equilibrium can be assumed, a simple procedure generates some of the alternative fitness sets.

Alleles↗
PubMed1989

Concern for environmental mutagens: some personal reminiscences.

This article is a personal, anecdotal account of the early days of concern for environmental mutagenesis. The history of the original National Academy of Sciences Committee on the Biological Effects of Atomic Radiations (BEAR) and its early controversies are reviewed, along with the initial establishment of principles for discovering potential chemical mutagens. Although it emphasizes the great advances in cellular and molecular understanding over the past 35 years, the article ends with a pessimistic assessment of any possibility of quantitative assessment of mutational impacts on future generations.

Carcinogens, Environmental↗