A gene family is a set of several similar genes. They occur by the duplication of a single original gene. Usually they have similar biochemical functions. The idea that genes get duplicated is almost as old as the science of genetics.[1]
One such family are the genes for human haemoglobin subunits. The ten genes are in two clusters on different chromosomes, called the α-globin and β-globin loci. These two gene clusters are thought to have arisen from a precursor gene being duplicated, about 500 million years ago.[2]
The biggest gene family is said to be the olfaction genes.[3] The homeobox genes are another important group.[4]
Genes for the immune system include several gene families. They code for the major histocompatibility complex,[5] and the immunoglobulins.[6] The toll-like receptors are the main sensors of infection in mammals.[7][8]