X CHROMOSOME DNA REPLICATION: DEVELOPMENTAL SHIFT FROM SYNCHRONY TO ASYNCHRONY.

The X chromosome in Melanoplus differentialis is negatively heteropycnotic in the early spermatogonial cell generations but positively heteropycnotic in the final premeiotic interphase. Autoradiography after administration of tritiated thymidine reveals that this condensation change is paralleled by a change in the time of DNA replication in the X chromosome relative to that in the autosomes.