Asynchronous DNA Replication in the Chromosomes of Haplopappus gracilis (2n=4)

Abstract

1. Chromosome 1 (V-shaped chromosome) of Haplopappus gracilis (2n=4) had three late-replicating regions located independently in the proximal regions of both arms, in a median region of the long arm and in a subdistal region of the long arm.
2. Chromosome 2 (J-shaped, satellited chromosome) of this species had two late-replicating regions situated in the proximal regions of both arms and in the satellite.
3. All of the late-replicating regions in the two pairs of chromosomes were found to be heterochromatic.
4. The duration of DNA replication in heterochromatins was found to be longer than that in euchromatins.
5. It was presumed that chromosome 1 was organized as a compound chromosome composed of three independently replicating segments.