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Sunday, 3 July 2011

Gene

Gene

The question of whether classical genetics could be (or already has been) reduced to molecular biology (to be taken up below) motivated philosophers to consider the connectibility of the term they shared: the gene. Investigations of reduction and scientific change raised the question of how the concept of the gene evolved over time, figuring prominently in C. Kenneth Waters' (1990, 1994, 2007, see entry on molecular genetics), Philip Kitcher's (1982, 1984) and Raphael Falk's (1986) work. Over time, however, philosophical discussions of the gene concept took on a life of their own, as philosophers raised questions independent of the reduction debate: What is a gene? And, is there anything causally distinct about DNA?
Falk (1986) explicitly asked philosophers and historians of biology, “What is a Gene?” Falk drew on Kenneth MacCorquodale and Paul E. Meehl's distinction between quantities that can be obtained by manipulating values of empirical variables without hypothesizing the existence of unobserved entities or processes (dubbed “intervening variables”) and concepts which assert the existence of entities and the occurrence of events not reducible to the observable (dubbed “hypothetical constructs”) (MacCorquodale and Meehl 1948). Employing this distinction, Falk claimed that the gene began as an intervening variable but morphed into a hypothetical construct with Morgan's chromosomal theory of inheritance and then with molecular biology, when the gene became equated with a sequence of DNA.
Discoveries such as overlapping genes, split genes, and alternative splicing (discussed in Section 1.2) made it clear that simply equating a gene with an uninterrupted stretch of DNA would no longer capture the complicated molecular-developmental details of mechanisms such as gene expression (Downes 2004). In light of the enormous complexity found in the process of moving from a stretch of DNA to a protein product, Falk's (1986) question persists: What is a gene? Two general trends have emerged in the philosophical literature to answer this question and to accommodate the molecular-developmental phenomena: first, distinguish multiple gene concepts to capture the complex structural and functional features separately, or second, rethink a unified gene concept to incorporate such complexity.

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