On the structure of gene control regions.

A model emphasizing the possible genetic role of tandem duplications of reverse repeats has been developed as an extension of Crick's (1971) general model for the chromosomes of higher organisms. Although developed initially (1) to explain why random differences in the control regions of individual gene loci might confer a selective advantage on heterozygous individuals as well as (2) to offer the species a means by which such differences might be effected without mutational harm, it seems that control regions built on a foundation of tandemly duplicated reverse repeats would exhibit many properties previously observed in studies on mutable loci in various organisms.