| Popis: |
THE constant deoxyribonucleic acid content per set of chromosomes1,2 and the close similarity of average base composition of deoxyribonucleic acid3 in various tissues in an animal species can be explained by assuming that the replication of all chromosomal deoxyribonucleic acid initially present in the fertilized ovum follows precisely the Watson–Crick model4 during the ontogenesis. Recent observations of Bendich et al. 5, however, revealed that deoxyribonucleic acid from one animal source is heterogeneous and can be represented as a ‘chromatographic profile’ as fractionated on an ‘Ecteola’ cellulose column6. Such profiles are different from one tissue to another even in a single mammalian species. The most remarkable difference was found between rat kidney and rat brain. This observation is difficult to reconcile with the Watson–Crick replication model, and suggests a pronounced differentiation of deoxyribonucleic acid during ontogenesis. In repeating the experiments of Bendich et al., we have obtained a different result, which will be described below. |
