Classical Genetics Theory Research Articles

A General Definition of the Heritable Variation That Determines the Potential of a Population to Respond to Selection

Genetic selection is a major force shaping life on earth. In classical genetic theory, response to selection is the product of the strength of selection and the additive genetic variance in a trait. The additive genetic variance reflects a population's intrinsic potential to respond to selection. The ordinary additive genetic variance, however, ignores the social organization of life. With social interactions among individuals, individual trait values may depend on genes in others, a phenomenon known as indirect genetic effects. Models accounting for indirect genetic effects, however, lack a general definition of heritable variation. Here I propose a general definition of the heritable variation that determines the potential of a population to respond to selection. This generalizes the concept of heritable variance to any inheritance model and level of organization. The result shows that heritable variance determining potential response to selection is the variance among individuals in the heritable quantity that determines the population mean trait value, rather than the usual additive genetic component of phenotypic variance. It follows, therefore, that heritable variance may exceed phenotypic variance among individuals, which is impossible in classical theory. This work also provides a measure of the utilization of heritable variation for response to selection and integrates two well-known models of maternal genetic effects. The result shows that relatedness between the focal individual and the individuals affecting its fitness is a key determinant of the utilization of heritable variance for response to selection.

Landscape refuges delay resistance of the European corn borer to Bt-maize: A demo-genetic dynamic model

We constructed a reaction-diffusion model of the development of resistance to transgenic insecticidal Bt crops in pest populations. Kostitzin’s demo-genetic model describes local interactions between three competing pest genotypes with alleles conferring resistance or susceptibility to transgenic plants, the spatial spread of insects being modelled by diffusion. This new approach makes it possible to combine a spatial demographic model of population dynamics with classical genetic theory. We used this model to examine the effects of pest dispersal and of the size and shape of the refuge on the efficiency of the “high-dose/refuge” strategy, which was designed to prevent the development of resistance in populations of insect pests, such as the European corn borer, Ostrinia nubilalis Hübner (Lepidoptera, Crambidae). We found that, with realistic combinations of refuge size and pest dispersal, the development of resistance could be considerably delayed. With a small to medium-sized farming area, contiguous refuge plots are more efficient than a larger number of smaller refuge patches. We also show that the formal coupling of classical Fisher–Haldane–Wright population genetics equations with diffusion terms inaccurately describes the development of resistance in a spatially heterogeneous pest population, notably overestimating the speed with which Bt resistance is selected in populations of pests targeted by Bt crops.

Elaborating the structures of a science discipline to improve problem-solving instruction: An account of Classical Genetics' theory structure, function, and development

Situating the conceptual knowledge of a science discipline in the context of its use in the solving of problems allows students the opportunity to develop: a highly structured and functional understanding of the conceptual structure of the discipline; general and discipline-specific problem-solving strategies and heuristics; and insight into the nature of science as an intellectual activity. In order realize these potential learning outcomes, the reconstructions of scientific theories used in problem solving must provide a detailed account of (1) realistic scientific problems and their solutions; (2) problem-solving strategies and patterns of reasoning of disciplinary experts; (3) the various ways that theories function for both disciplinary experts and students; and (4) the way theories, as solutions to realistic scientific problems, develop over time. The purpose of this paper, therefore, is to provide further specificity regarding a philosophical reconstruction of the structure of Classical Genetics Theory that can facilitate problem-solving instruction. We analyze syntactic, semantic and problem-based accounts of theory structure with respect to the above criteria and develop a reconstruction that incorporates elements from the latter two. We then describe how that reconstruction can facilitate realistic problem solving on the part of students.