Size and structure of the bird genome. II. Repetitive DNA and sequence organization.

1. Highly repetitive, middle repetitive and single copy DNA were evaluated in 19 species of birds, belonging to nine orders, by means of a reassociation kinetics method. 2. A rather uniform pattern is present in all the species studied (single copy = 60-75%; middle repetitive = 13-20% and highly repetitive 10-20%). 3. Reassociation kinetics of fragments of different length confirms the presence of a long period interspersion pattern. 4. Among different orders, no significant differences are observed. 5. DNA sequence organization seems to be related to genome size, with an inverse correlation between DNA nuclear content and amount of interspersed repetitive sequences.