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THE PHENOTYPIC DECEPTION: INFLUENCES OF CLASSICAL GENETICS ON GENETIC PARADIGMS THOMAS A. FOGLE* What does it mean to say that a trait is "genetic"? The public view of the genotype-phenotype relationship is oversimplified and does not capture the complexity of molecular events as revealed by modern biology. With the advent of knowledge about jumping genes (transposons), coding regions (exons) that can be spliced together in more than one combination to produce multiple gene products, and nucleotide sequences that are part of two reading frames (overlapping genes), genes can no longer be visualized as simply a series of fixed, discrete units. Historically, the structure of the gene remained a mystery until the spiral staircase model of DNA structure was made famous by Watson and Crick [I]. Today, there is broad public awareness that DNA constitutes the hereditary material, while awareness of gene function more closely fits the term "factor" as used by geneticists during the classical period prior to 1920. Simple dichotomous phenotypes such as red- or white-eyed DrosophiL· and round or wrinkled peas serve as examples for expression of a typical gene. The price paid for this kind of either/or paradigm of genetic understanding is high because it fixates thinking on individual units (genes) as being causal in a simple and straightforward manner that ignores the lesson of complexity that modern genetics is unraveling. But is there really a false public perception ofthe genotype-phenotype relationship? A group of recent high school Westinghouse winners was asked to predict future directions in science. Among the high-tech wonders imagined was the suggestion that we will be able, at some point in the future, to create perfect humans by gene manipulation. Behind this fix-it-by-tinkering strategy lies a deeper, more subtie conceptualization that is both widespread and profoundly misleading. ?Department of Biology, Saint Mary's College, Notre Dame, Indiana 46556.© 1987 by The University of Chicago. AU righs reserved. 0031-5982/88/3101-0557$01.00 Perspectives in Biology and Mediane, 31, 1 · Autumn 1987 \ 65 As discoveries in molecular biology outstrip the ability of the public to absorb them, understanding the relationship between genes and organismal phenotypes remains static, if not antiquated, and betrays its Cartesian foundations of mechanistic functioning. Like a car with definable and nameable parts, so each organism is envisioned as consisting of units, layered into levels of organization: molecules, cells, organs, organism. A reductionist framework such as this, productive for empirical approaches to solving biological problems, is insufficient for integrative explanations of vital systems. A tacit assumption in molecular biology is that DNA is the stuff of which genes are made, and that a cause-and-effect relationship exists between the gene and its phenotype at each level of organization. Genes are not only a coded sequence of nucleotides but have also become the explanation as to why the phenotype has a particular set of characteristics . That is, the phenotype is mapped onto a gene which has a causal role in its expression. The question of interest becomes, Why are genes so often typified as discrete entities endowed with highly predictable and mechanistic expression? Put another way, why do talented high school science students believe that you can easily cut and paste the genome as if genes were parts that can be rearranged and expect a precise and replicable outcome? I begin by delving into one example of genetic misunderstanding to demonstrate that the problem originates with the scientific community and then proceed to discuss relevant historical events from the early classical period of genetics (1900-1920) to account for that outcome. The Tongue-Rolling Legend Old saws are hard to throw away. Tongue rolling, "the ability to curl the tongue into a longitudinal trough" [2], has long been used in biology classrooms as an example of a dominandy inherited Mendelian trait. First described by Sturtevant [3], it has been investigated by numerous authors, the most recent of whom has been Coreos [2]. He analyzed hundreds of pedigrees and found discrepancies in the Mendelian expectations (tongue rollers whose parents were nonrollers). He then reanalyzed the data from previous studies that used monozygotic and dizygotic twins. Because monozygotic twins have identical genotypes, it...


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