 Falk (1986) explicitly asked philosophers and historians of biology, “What is a Gene?” 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; Luc-Germain, Ratti and Boem 2015). In an effort to answer Falk’s question, two general trends have emerged in the philosophical literature: 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. (For a survey of gene concepts defended by philosophers, see Griffiths and Stotz 2007, 2013.; Rheinberger and Muller-Wille 2018)