EVOLUTION BY THE BIRTH-AND-DEATH PROCESS IN MULTIGENE FAMILIES OF THEVERTEBRATE IMMUNE-SYSTEM

Concerted evolution is often invoked to explain the diversity and evol ution of the multigene families of major histocompatibility complex (M HC) genes and immunoglobulin (Ig) genes, However, this hypothesis has been controversial because the member genes of these families from the same species are not necessarily more closely related to one another than to the genes from different species, To resolve this controversy, we conducted phylogenetic analyses of several multigene families of t he MHC and Ig systems. The results show that the evolutionary pattern of these families is quite different from that of concerted evolution but is in agreement with the birth-and-death model of evolution in whi ch new genes are created by repeated gene duplication and some duplica te genes are maintained in the genome for a long time but others are d eleted or become nonfunctional by deleterious mutations. We found litt le evidence that interlocus gene conversion plays an important role in the evolution of MHC and Ig multigene families.