CHROMOSOME BREAKAGE AND COMPLETE GENIC MUTATION PRODUCTION IN MOLECULAR TERMS

The current mutation theory required revision in the light of recent knowledge of the repairing system operative in a cell. The mechanism producing chromosome aberrations is discussed. The appearance of chromosome breakage is considered in relation to the activity of repairing systems in a cell, the dark-repair system in particular. Failure to understand how the breakage of one DNA strand in the chromosome structure is transferred to the other strand is the primary puzzle for interpreting the causes of chromosomal breakage, especially without DNA replication. This problem may be solved if one assumes that errors made by the repairing enzyme lead to the excision of the complementary region rather than of the region actually damaged, and that the gap made will remain and not be corrected by resynthesis. As a consequence, the second contact with repairing endonucleases will result in cutting of DNA in the vicinity of the damaged region which will cause breakage of the molecule. The same mechanism seems responsible for production of full and mosaic mutations as well as for translocation, inversion and deletion. © 1969.