On simple repeated GATCA sequences in animal genomes: a critical reappraisal

Simple tandemly organized GATCA sequences occurred in all eukaryotic genomes investigated. The amount and organization of individual GATCA sequences or derivatives thereof vary considerably in animal DNAs and can be assessed by simple but specific hybridization procedures with chemically pure oligonucleotide probes. In several animal species, including humans, GATCA sequences show extensive polymorphism, thus allowing individual-specific "DNA fingerprints." In selected rodents the sex-chromosomal organization of GATCA sequences is being studied extensively, revealing rapid evolutionary changes. In addition, insight can be expected into the sequences involved in obligatory meiotic crossing over between the X and Y chromosomes, into unequal crossing-over events, and into the linkage of GATCA elements to male-specific as well as to male-determining genes on the Y chromosome. The exact provenance of GATCA sequences in present-day eukaryotes cannot be pinpointed, but evolutionary conservation and several modes of de novo generation are discussed. Among these are unequal recombination, slipped strand mispairing, and other unspecified mechanisms. The latter include inherent properties that are responsible for the "selfish" or "ignorant" nature of simple repeats. Expression, if any, of GATCA sequences is critical to the overall significance of these ubiquitously interspersed simple repeats.