Similar size of the replicons in Chironomus polytene chromosomes at two developmental stages.

The size of the DNA replication units in salivary gland polytene chromosomes of Chironomus arvac at 2 developmental stages (red-head and late 4th instar) was investigated. The 2 developmental stages differ with respect to intensity of DNA replication with much lower values at the red-head stage. Also the level of polytenization is lower at the red-head stage. The size of the replication units was measured by determining the size of double-stranded DNA fragments released from active replication units during the cell lysis. At both stages it is possible to release from the polytene chromosome a double-stranded DNA fragment of similar size. This indicates that there is no or very little difference in size of active replication units in the same tissue at the 2 developmental stages.