Chick embryo DNA: the isolation and identification of the repeated and non-repeated sequences and their hybridization with chromosomal RNA

Three families of chick embryo DNA have been characterized and it has been shown that the most rapidly reannealing sequences (R family) are complementary to chromosomal RNA; material which fulfills the requirements of an activator RNA. This information suggests that at least some of the genome may be organized as envisioned by Britten and Davidson (1969). The principle objection to their hypothesis comes from the belief that natural selection and the deleterious mutation rate per gene locus per generation significantly limits the number of functional genes which can be maintained within the genome. The suggestion is made that the S family, comprising 65% of the "total number of sequences, may be involved in the pairing of homologous chromosomes. The idea that the majority of the DNA is non-functional is rejected.