Abstract
Published data on the pattern and genetic control of early cleavage divisions in Drosophila melanogaster are summarized. Data on chromosome elimination induced by the mutation paternal loss (pal), elimination of ring and rod chromosomes, and mitotic exchanges in the hyperploid pronucleus in Drosophila suggest a specific structural role of heterochromatic chromosomal regions during early cleavage. Mutations disturbing early cleavage divisions include mutations with effects assigned to different stages of this process. This allows us to suggest the existence of isofunctional proteins involved in mitosis and alternating during early cleavage. In addition, cleavage divisions apparently include a special mechanism preserving primordia of germ tissue from unbalanced nuclei.
