Quantitative analysis of DNA content in the salivary gland chromosomes of Chironomus thummi at larval and prepupal stages.

Relative DNA content during the polytenization of the salivary gland nuclei of Chironomus thummi was measured by cytophotometric and cytofluorometric methods. To estimate the degree of polyteny, the DNA content was calculated in hemocyte and spermatocyte nuclei. Chromosome polytenization is associated with 10 to 12 replication rounds. There are 4-5 replication rounds in 1st instar, 2-3 rounds in 2nd instar; 3rd and 4th instars have 1-2 rounds each. From early postembryonic development, larvae already have salivary gland nuclei representing two polyteny classes (2-3 - 2-4C); A similar heterogeneity is retained in all instars. The approximate DNA content is 0.51-0.58 picogram per diploid set.