A gene family is a set of genes defined by presumed homology, i.e. evidence that the genes evolved from a common ancestral gene. They generally share some biochemical activity. Genes are generally categorized into families based upon shared sequence motifs and similarities in structure. Phylogenetic techniques can be used as a more rigorous test. The positions of introns within the coding sequence can be used to infer common ancestry. Knowing the sequence of the protein encoded by a gene can allow researchers to apply methods that find similarities among protein sequences that provide more information than similarities or differences among DNA sequences. Furthermore, knowledge of the protein's secondary structure gives further information about ancestry, since the organization of secondary structural elements presumably would be conserved even if the amino acid sequence changes considerably. These methods often rely upon predictions based upon the DNA sequence. This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... In biology, two or more structures are said to be homologous if they are alike because of shared ancestry. ... Biochemistry is the chemistry of life. ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ... Diagram of the location of introns and exons within a gene. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ... A representation of the 3D structure of the Myoglobin protein. ... An amino acid residue is what is left of an amino acid once a molecule of water has been lost (an H+ from the nitrogenous side and an OH- from the carboxylic side) in the formation of a peptide bond. ...

If the genes of a gene family encode proteins, the term protein family is often used in an analogous manner to gene family.

See also: List of gene families, phylogenetic tree This is a list of gene families or gene complexes, that is sets of genes which occur across a number of different species which often serve similar biological functions. ... It has been suggested that Evolutionary tree be merged into this article or section. ...