Evolutionary sequence divergence within repeated DNA families of higher plant genomes. II. Analysis of thermal denaturation.

An assay based on derivative analysis of thermal denaturation (melting) behavior of reassociated DNA was developed in an attempt to characterize the sequence relationships in repeated DNA families according to the homogeneous or heterogeneous models of Bendich and Anderson (1977). The validity of the technique was confirmed by the use of deaminated Escherichia coli DNA models for repetitive families. The melting data for DNA reassociated at two different temperatures provided strong evidence that Pisum sativum repeated families are mostly heterogeneous, while homogeneous families predominate in Vigna radiata. These findings, together with other differences between the two genomes, suggest that the rate of sequence amplification has been higher in the evolutionary history of Pisum DNA. A general trend seems to exist for high amplification rates in large, highly repetitive plant genomes such as Pisum and lower rates in smaller plant genomes such as Vigna, as well as in the generally smaller, less repetitive genomes of most animal species.