Insect sex chromosomes. IV DNA replication in the chromosomes of Gryllotalpa fossor.

In Gryllotalpa the cell cycle duration in the hepatic caecae in vivo is about 12.5 h and of various phases are, G2 + P about 10 h, S about 2.5--3.5 h, and G1 appears negligible or absent. These estimates of the cell cycle are the only ones available in Gryllotalpidae. In the female Gryllotalpa, as in mammals, there is asynchronous DNA replication between the two euchromatic arms of the two X chromosomes. The other arm is constitutively heterochromatized and as expected is late replicating. Thus, a regulatory mechanism for dosage compensation by X chromosome inactivation appears to be operating in Gryllotalpa. This we believe, is the first cytogenetic demonstration of such a mechanism outside mammals.