Chromosome Aberrations caused by Radioactive Thymidine

CHROMOSOME aberrations in onion root tips treated with 2- 14 C-thymine deoxyriboside (thymidine) and with 2- 14 C-thymine have been studied. It has been found that radioactive thymidine gives a significantly higher frequency of aberration than equivalent amounts of radioactive thymine. Since thymidine is a precursor of deoxyribonucleic acid thymine 1,2 and becomes a part of the deoxyribonucleic acid structure without diversion to any known cyto-plasmic component including ribonucleic acid, a unique system is available for provoking intranuclear damage. Thymine, on the other hand, is not incorporated into deoxyribonucleic acid 2,3 . Its radiation effects, therefore, have been studied because it enters the cell without becoming a part of deoxyribonucleic acid and thus provides a source of radiation outside the deoxyribonucleic acid molecule.