ABSTRACT
Primary studies on whole sequenced genomes focused on single genes and little attention was directed to repetitive DNAs, and duplicated segments. Single- and few-copy sequences correspond to a small fraction of the genomes. The repetitive sequence importance in gene regulation and chromosome physiology may be illustrated by mutations in some minisatellite sequences that may contribute to as many as 10% of all cases of breast, colorectal and bladder cancer, and acute leukemia. Repetitive DNAs include the tandemly-arrayed satellite, minisatellite and microsatellite sequences, and dispersed repeats such as transposons and retrotransposons. Studies of the repetitive fraction of the genome can contribute to the knowledge of the complex organization of DNA in the cell nucleus. Concerning chromosomal organization of repetitive DNA sequences, one of the most studied fractions of the fish genome is the satellite DNA.
