Abstract
In analytical centrifugation of partially renatured Drosophila hydei DNA, a fast re-associating DNA fraction appears in a density position identical to the density of native bulk DNA. A comparison of the density patterns of partially re-associated DNA from animals of different genetic constitution reveals that a large proportion of this highly repetitive DNA is located in the heterochromatic arm of the X chromosome, and that more than 60% of the DNA in this chromosome region is highly repetitive. Only a small proportion (less than 15%) of the DNA of the heterochromatic Y chromosome is composed of highly repetitive sequences. The autosomes contain more than 80% of the DNA of the genome, but less than 10% of this DNA represents highly repetitive nucleotide sequences. Hybridizing in vitro synthesized [ 3H]RNA across DNA density gradients shows that the apparently uniform main band of native DNA includes several highly repetitive DNA fractions (“cryptic” satellites). One of these, occupying a central position in the bulk DNA band, is identical with the highly repetitive fraction located in the X chromosome.
Published Version
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