The Content of Deoxyribonucleic Acid in Individual Polytene Chromosomes of Chironomus tentans

Abstract

The DNA content was measured in individual polytene chromosomes of Chironomus tentans belonging to the two last classes of replication. The following results were obtained: (1) The DNA contents of the chromosomes of the higher size class were about twice that of the lower class, which indicates that most or all of the chromatids carry out one replication between these two stages. (2) The DNA contents were found to be correlated to chromosome length, and the average amount of DNA per band was similar in the four chromosome pairs. (3) The probable DNA value per chromatid set was determined, from which the average DNA value per chromomere could be estimated to 10-16 g. This value corresponds to about 105 base pairs, suggesting either that the bands represent operational units of great complexity or that a large part of DNA is non-functional in an informational sense.