GENOME MAPS 8:
Building Gene Families
Genome sequencing projects and other large-scale efforts are generating hundreds of thousands of sequences of new proteins from diverse organisms. The task of discovering the structure and function of an unknown protein is aided by the fact that most new genes are related to other genes, and these relationships can often be detected via sequence similarity. Perhaps half of all known genes encode members of some 3000 major families. Family members share sequence and structural similarities, suggesting divergence from a common ancestor. Unlike proteins that are direct counterparts in different organisms, there can be many members of a gene family within one organism that carry out distinct, yet similar, functions. For the organism itself, the existence of gene families provides a way of generating diversity in function and specificity from a limited number of building blocks, which is essential for the evolutionary success of a genome. Within large eukaryotic genomes, gene family size varies tremendously, ranging from a unique member to thousands of members. Even smaller genomes harbor families that comprise several percent of their genome.
