Extent of DNA homology in some distantly and intimately related fishes

Graduation date: 1973An attempt was made to differentiate between runs of steelhead by comparing the reassociations of their DNA. Conditions for the reassociation were studied using E. coli DNA, and observations\ud were made spectrophotometrically. Of the five buffers examined, 1.0 molar sodium perchlorate plus one-hundredth molar tris-HCl, pH 7.1, at 60° or 70°C produced the fastest reassociation rates\ud of 40,000 psi sheared DNA, over ten times faster than that of 0.12 molar sodium phosphate, pH 6.8. The rate increase was necessary for observation of the very slowly reassociating DNA. The genomes of the chinook jack, steelhead, and starry flounder were characterized and compared with respect to the composition of repeated sequences, similarity in base sequencing, and the amount of information in the nonrepeated sequences. The steelhead has a large, highly repeated fraction, sequences repeated at many intermediate frequencies, and a nonrepeated portion comprising 20-40% of the total and having a complexity greater than 2x10⁹ nucleotide pairs. Chinook DNA was quite similar but had distinct differences in the base sequencing of the less repeated region. Flatfish DNA differed greatly from that of the steelhead. The amount of the nonrepeated DNA was two thirds of the total while the complexity was only 1x10⁹. There was no significant amount of DNA repeated at intermediate frequencies, and there were no measurable sequence similarities. The DNA from the Rogue River, the Siletz River, and Sashin Creek steelhead had no differences measurable by the techniques used