Changes in the thermal denaturation profiles of DNA from different developmental stages of the newt Triturus vulgaris.

The melting profiles of DNA samples from the early gastrula and early neurula of Triturus vulgaris are essentially the same, whereas DNA from mid to late gastrula possesses higher Tm values and shows a deviation from the regular sigmoidal shape at temperatures above Tm. The plot on normal probability paper indicates a second DNA fraction which melts at higher temperatures and, consequently, it has a higher GC-content than the bulk of DNA. These facts confirm our idea that differential DNA replication occurs during gastrulation.