Insect sex chromosomes, XI. 3H-TdR induces random aberrations in the X chromosome(s) of Gryllotalpa fossor (Orthoptera).

The pattern of titrated thymidine (3H-TdR), a direct precursor of DNA, induced aberrations on the X chromosome of Gryllotalpa fossor was examined. 3H-TdR produced aberrations randomly distributed over the entire length of the X chromosome; breaks were observed in both the eu- and the heterochromatic arms of the X chromosome in both the sexes. Since the eu- and the heterochromatic arms cannot be distinguished cytologically in this insect, the presence of aberrations on both arms of the same X chromosome in the male and damage to both X chromosomes in the female indicate that both euchromatic and heterochromatic regions (facultative or constitutive) are equally liable to aberrations induced by H-TdR. This is in contrast to the non-random induction of aberrations by 3H-UdR, which causes chromosome damage due to the proximity of the labeled RNA to the DNA template during transcription.