 The first part of this entry provides a historical overview, which serves as a background to understand philosophical accounts of scientific change with respect to genetics addressed in the second part. Section 2.1 will discuss models of theory reduction in genetics. Sections 2.2 and 2.3 will address discussions of change and diversification in the meaning and reference of the term “gene”. Because of its central role in most areas of biology, the gene concept also has a central role in debates in philosophy of biology (see entries on  philosophy of biology  and   feminist philosophy of biology).  This entry focusses on the gene concept in studies of heredity and development. Additional philosophical problems concerning the concept of genetic information, causation, and determinism are covered in entries on  biological information,  genetics,  molecular genetics,  molecular biology,  the distinction between innate and acquired characteristics,  and  the human genome project  (see also Griffiths &amp; Stotz 2013). For conceptual questions pertaining to genes as central units of evolution, the reader is referred to the entries on  evolution,  ecological genetics,  population genetics,  genetic drift,  units and levels of selection,  and  replication and reproduction  (see also Sterelny &amp; Griffiths 1999).