Definition: A gene is an ordered sequence of nucleotides located in a particular position (locus) on a particular chromosome that encodes a specific functional product (the gene product, i.e. a protein or RNA molecule). It includes regions involved in regulation of expression and regions that code for a specific functional product. See gene expression, allele.

Human genome comprises between 20000 and 29000 genes.

Features

 housekeeping genes
 cancer genes

• oncogenes
• tumor suppressor genes

Pathology (genic anomalies)

 quantitative genic anomalies

• genic overexpression
  • genic amplification
  • translocation downstream of an active promoter
  • numerical chromosomal anomalies (trisomies, tetrasomies)

• genic underexpression
  • genic inactivation
    • numerical chromosomal anomalies (deletions)
    • mutations of gene promoter
    • methylation of gene promoter

 qualitative genic anomalies (genic mutation)

• proteic loss of function
  • genic deletion
  • point mutation

• genic activation (proteic gain of function)
• fusion genes (fusion proteins)

Historics

The term coined by Johannsen (1909) for the fundamental physical and functional unit of heredity. The word gene was derived from De Vries' term pangen, itself a derivative of the word pangenesis which Darwin (1868) had coined.

See also

 cancer genes

• oncogenes
• tumor suppressor genes

References

 Carlson EA. Defining the gene: an evolving concept. Am J Hum Genet. 1991 Aug;49(2):475-87. PMID: #1867208#