Cited by 2.8k
Hundreds of thousands of copies of DNA sequences have been incorporated into the genomes of higher organisms.
California Institute of Technology
Publishes on RNA and protein synthesis mechanisms, DNA and Nucleic Acid Chemistry, Marine and coastal plant biology. 231 papers and 23.9k citations.
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Hundreds of thousands of copies of DNA sequences have been incorporated into the genomes of higher organisms.
Cell differentiation is based almost certainly on the regulation of gene activity, so that for each state of differentiation a certain set of genes is active in transcription and other genes are inactive. The establishment of this concept (1) has depended on evidence \nindicating that the cells of an organism generally contain identical genomes (2). Direct support for the idea that regulation of gene activity underlies cell differentiation \ncomes from evidence that much of the genome in higher cell \ntypes is inactive (3) and that different ribonucleic acids (RNA) are synthesized in different cell types (4).
Recent experimental information on DNA sequence repetition is reviewed, and the significance of both repetitive and non-repetitive sequence considered. Included are a summary of data on the distribution of genome sizes in animals, new experiments on interspecific DNA homology, the distribution of sequence frequencies, and the interspersion of repetitive sequences within the genome. Aspects of the process of evolution are considered at the level of change in the DNA. the process by which novel structure and function could have arisen during evolution are considered speculatively in terms of the authors' gene regulation theory (Britten and Davidson, 1969).
The mutation rates of DNA sequences during evolution can be estimated from interspecies DNA sequence differences by assaying changes that have little or no effect on the phenotype (neutral mutations). Examination of available measurements shows that rates of DNA change of different phylogenetic groups differ by a factor of 5. The slowest rates are observed for higher primates and some bird lineages, while faster rates are seen in rodents, sea urchins, and drosophila. The rate of DNA sequence change has decreased markedly during primate evolution. The contrast in rates of DNA sequence change is probably due to evolutionary variation and selection of biochemical mechanisms such as DNA replication or repair.