Deoxyribonucleic Acid

Abstract

Because of the ease of its extraction, DNA from sea urchin sperm has been used for many important studies. Indeed, Chargaff, used DNA from sea urchin sperms to establish his rules on the equivalence of A + G and T + C (see Chargaff and Davidson, 1955). It was also with sea urchin sperm DNA that Britten and Kone (1968) established some of their evidence for the existence of repetitive sequences. A series of subsequent papers have illuminated the general organization of the sea urchin genome. Weinblum et al., (1973) analyzed the kinetics of DNA reannealing and concluded that up to 19% of Sphaerechinus granulans DNA contains sequences repeated 800 times, with a kinetic complexity of 1.8×10⁵ nucleotide pairs (b.p.); 31% of DNA contains sequences repeated 100 times, with a kinetic complexity of 1.7×10⁶ b.p.; 20% of the DNA contains sequences repeated 3 times, with a kinetic complexity of 5.2×10⁸ b.p.; and 30% of the DNA contains unique sequences, with a kinetic complexity of 2.3×10⁸ b.p. Further analyses (Graham et al., 1974) have established that about 50% of genome of Strongylocentrotus purpuratus contains unique sequences 1.2–1.5×10³ b.p. long separated by repeated sequences 300–400 b.p. long; 20% is organized as above, but is made of longer sequences, the repeats of which have little homology with the shorter repeats (Eden et al., 1977); 22% is made of unique sequences, with little or no repeats interspersed; and 6% is made of longer repeated sequences (Fig. 4.1).