Evolution of the Immunoglobulin Supergene Family

The many cell surface and soluble molecules of
the immune system that mediate different
functions such as recognition, binding, or adhesion
of specific molecules showmany structural
similarities. Some parts are found outside the
immune system. As a group, they constitute a
gene superfamily, derived from an ancestral
gene common to all members. The homologies
of the domains of their gene products and of
their gene sequences can be explained by evolutionary
origin from a common ancestral gene.
The Ig gene family members code for immunoglobulin
domains, usually of about 70–110
amino acids homologous with an Ig variable (V)
or constant (C) domain. Each Ig domain is
derived from conserved DNA sequences.