Nucleotide sequence and genomic organization of cichlid fish minisatellites.

We have cloned, sequenced, and determined the genomic organization of minisatellites from the African cichlid fish, Oroechromis niloticus. We estimate that minisatellites related in sequence to the Jeffreys' core probes 33.6 and 33.15 occur approximately every 1000 kilobase pairs in the cichlid fish genome. Sequencing of three minisatellites revealed that the size of the monomer units of the tandem arrays ranged from 7 to 24 base pairs (bp). One minisatellite appeared to contain a higher ordered periodicity of 90-120 bp superimposed on the apparent 15 bp monomer repeat, indicating a particularly large unit of homogenization for a minisatellite array. Sequence heterogeneity of repeat units within tandem arrays varied considerably from one minisatellite to another. Hybridization of cloned minisatellites to genomic DNA of cichlid fishes generated, in most instances, multilocus fingerprint patterns, indicating that families of minisatellites related by sequence exist in the cichlid genome. Two minisatellite clones, however, generated polymorphic single locus fingerprints, suggesting that these loci are conserved in closely related African cichlids. The cross hybridization of these cichlid minisatellites within and between related taxa, as well as to unrelated fish species such as Atlantic salmon (Salmo salar), complement the human minisatellite sequences for the study of genetic relationships among individuals from a wide range of fish species.