SEQUENCE ORGANIZATION AND EVOLUTION, IN ALL EXTANT WHALEBONE WHALES, OF A DNA SATELLITE WITH TERMINAL CHROMOSOME LOCALIZATION

A heavy (GC rich) DNA satellite with terminal chromosomal localization is characteristic for all mysticete (whalebone whale) genomes. Sequen ces of 58 repeats of the satellite were compared in all ten extant mys ticete species. In three families comprising eight species, the typica l repeat length was 422(421) bp. In two species, the northern right wh ale and the bowhead, of family Balaenidae (right whales) the repeats w ere much longer, typically ca. 900 and ca. 1200 bp. In all species the repeats were composed of a unique portion of constant length (212/211 bp), and a subrepeat portion, the length of which was variable. The e volutionary rigidity of the unique portion of the repeat is contrasted by the pronounced length variability of the subrepeat portion. The su brepeat portion consists essentially of 6 bp motifs, such that length differences are usually in multiples of 6 bp. The motif TTAGGG constit uted 35% 50% of the subrepeats. Comparison between the unique portion of the 58 sequenced repeats revealed that the repeats divided into two primary groups, one comprising the two balaenids, the other including the eight remaining species. The mean difference between the two grou ps averaged 8.4%. In this sequence comparison the repeats of the pygmy right whale constituted a group that was separated from repeats of th e other species. In all other cases repeats were intermingled to some extent between species. Comparison of individual repeats suggests that the unique portion evolves in concert, at a slow rate. A neighbor-joi ning comparison between the consensuses of all species suggests that t he unique portion of the repeats evolves at a somewhat different rate in different lineages.