Behavior genetics and postgenomics

Abstract

The science of genetics is undergoing a paradigm shift. Recent discoveries, including the activity of retrotransposons, the extent of copy number variations, somatic and chromosomal mosaicism, and the nature of the epigenome as a regulator of DNA expressivity, are challenging a series of dogmas concerning the nature of the genome and the relationship between genotype and phenotype. According to three widely held dogmas, DNA is the unchanging template of heredity, is identical in all the cells and tissues of the body, and is the sole agent of inheritance. Rather than being an unchanging template, DNA appears subject to a good deal of environmentally induced change. Instead of identical DNA in all the cells of the body, somatic mosaicism appears to be the normal human condition. And DNA can no longer be considered the sole agent of inheritance. We now know that the epigenome, which regulates gene expressivity, can be inherited via the germline. These developments are particularly significant for behavior genetics for at least three reasons: First, epigenetic regulation, DNA variability, and somatic mosaicism appear to be particularly prevalent in the human brain and probably are involved in much of human behavior; second, they have important implications for the validity of heritability and gene association studies, the methodologies that largely define the discipline of behavior genetics; and third, they appear to play a critical role in development during the perinatal period and, in particular, in enabling phenotypic plasticity in offspring. I examine one of the central claims to emerge from the use of heritability studies in the behavioral sciences, the principle of minimal shared maternal effects, in light of the growing awareness that the maternal perinatal environment is a critical venue for the exercise of adaptive phenotypic plasticity. This consideration has important implications for both developmental and evolutionary biology.Keywords: behavior genetics; developmental biology; evolutionary developmental biology; epigenetics; evo-devo; gene association studies; genetics; heritability; maternal effects; phenotypic plasticity; stochasticity; twin studies A paradigm shiftIt is one of the aims of any scientific discipline to construct models that will account for as many observations as possible within a coherent framework. These models, and the framework of which they are a part, constitute a scientific paradigm. A paradigm commonly includes a set of dogmas, or key assumptions concerning both the nature of certain phenomena and the methodologies employed to study them that are never doubted as long as the paradigm appears to work well. The history of science, as it turns out, is a history of overturned dogmas and supplanted paradigms (Kuhn 1970). The discovery of new phenomena -anomalies -that appear to violate a central dogma or dogmas -perhaps, according to the paradigm, they have been deemed incapable of existing -can constitute a serious challenge to a paradigm. Sometimes, these phenomena can...

The effects of learning about one’s own genetic susceptibility to alcoholism: a randomized experiment

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“…This failure has raised serious doubts about the validity of behavioral genetics studies reporting strong heritability for most phenotypes. It appears that the high heritabilities found in these studies were due in large measure to methodological deficiencies associated with the twin study method and to a faulty conceptual model that incorrectly assumed that genes exert main effects that are independent of the effects of the environment (Burt and Simons 2014;Charney 2012) Finally, contrary to the gene-centric model, evidence suggests that only about 2 % of the human genome codes for proteins (Carey 2012), while most of the remaining non-protein coding DNA (what used to be considered junk DNA) is involved in regulatory processes that determine which protein coding segments of a gene will be expressed and the types of proteins that will be produced (Meloni 2014;Pennisi 2012). Such findings have fostered a paradigmatic shift that places less emphasis upon inherited DNA differences between people and more importance upon identifying the epigenetic factors that control or regulate DNA expression.…”

The Role and Sources of Individual Differences in Critical-Analytic Thinking: a Capsule Overview

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