Frontiers of the biological sciences

Relations among fields: Mendelian, cytological and molecular mechanisms

Philosophers have proposed various kinds of relations between Mendelian genetics and molecular biology: reduction, replacement, explanatory extension. This paper argues that the two fields are best characterized as investigating different, serially integrated, hereditary mechanisms. The mechanisms operate at different times and contain different working entities. The working entities of the mechanisms of Mendelian heredity are chromosomes, whose movements serve to segregate alleles and independently assort genes in different linkage groups. The working entities of numerous mechanisms of molecular biology are larger and smaller segments of DNA plus related molecules. Discovery of molecular DNA mechanisms filled black boxes that were noted, but unilluminated, by Mendelian genetics.

The Canadian Rutherford lecture. An evolutionary view of disease in man

It is said that genes propose and experiences dispose. Biological adaptation (to fit with the experiences of life) implies functional and structural homeostasis. Disadaptation (the undoing of fitness, that is, morbidity, disease) occurs when experience overwhelms homeostasis or phenotypic variation undermines it. Human disease has social and cultural contexts, but it is also measurable in the biological dimensions of viability, development, reproduction, and longevity. Heritability is a description of ‘cause’ and, for some classes of disease, heritability is high in modern society relative to the past. Mendelian variation in man is immense; 90% of that occurring in single-copy DNA and associated with disease (selective mutation) is expressed in pre-reproductive life in the universal environment. Neutral (non-selective) mutations also occur in both coding and non-coding DNA regions; when the latter are tightly linked with selective mutations they can be used as markers of risk for disease. Accordingly, molecular genetics and other methods for defining genotype provide ways to anticipate risks to health and to prevent disease. To See a World in a Grain of Sand And a Heaven in a Wild Flower Hold Infinity in the palm of your hand And Eternity in an hour

A tentative molecular-biological hypothesis for arteriosclerosis

In view of the fact that complications of arteriosclerosis are the most frequent causes of death in industrialized societies, its etiology is of enormous interest. The widely held lipid theory (detrimental effects of cholesterol) has been attacked because it cannot account for such facts as the homeostatic relationship of endogenous and exogenous cholesterol: for the "normal" cholesterol content of the early atheroma; for the distribution of the lesions, their spotty occurrence and their "programmed" appearance. Arteriosclerosis is part of the normal processes of aging which are related to molecular-biological changes. Autoimmune processes and the effects of extrachromosomal organisms of the genome (viruses, plasmids, viroids) are clinically of interest. Arteriosclerotic lesions are probably influenced by autoimmune processes; the variability and specificity of the non-chromosomal organisms may explain the location of the lesions; the end of the incubation period of the organisms may be responsible for the programmed appearance of clinical symptoms. The lipid changes are probably part of the adaptive mechanisms counteracting the rapid destruction of the vessels following the DNA alterations. Arteriosclerosis is part of normal evolution.