The definition of a gene as a discrete unit of heredity has developed since the work of Mendel, from the recognition of a gene as a blueprint for a protein, to a transcribed code in the nucleic acid sequence, to a DNA sequence possessing particular characteristics allowing widespread annotation of the genome (Fig 1.3). The 'protein-centric' view of a gene has required adaptation with the recognition that there are many sites of transcription in the genome that lead to RNA but do not result in translation into a protein ('noncoding RNA'). Such transcriptionally active regions are involved in a diverse array of predominantly regulatory functions. The very extensive use of alternative splicing (Section 11.6) and the presence of many transcriptional start sites further complicate our view of a 'gene'. Gerstein and colleagues note that a gene must encompass the concept that there is a genomic sequence encoding a functional RNA or protein product: where a number of functional products share overlapping genomic sequences a coherent union of all is considered (Gerstein etal. 2007).
A gene as a discrete 1900
heritable unit determining particular characteristics
A gene as a distinct locus
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