When Does a Sequence Count as a Gene?

Extract

The number of genes depends in part on how a gene is defined. In the human genome, with its introns and pseudogenes and “junk DNA,” it is not always readily apparent which sequences are truly genes.

The National Human Genome Research Institute Web site (http://www.nhgri.nih.gov) defines a gene simply as, “The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein.”

According to the Genesweep rules, “A gene is a set of connected transcripts. A transcript is a set of exons via transcription followed (optionally) by pre-mRNA splicing. Two transcripts are connected if they share at least part of one exon in the genomic coordinates. At least one transcript must be expressed outside of the nucleus and one transcript must encode a protein.”