Abstract
The mutaion rate of the unstable strain T4001 of Ustilago maydis w as determined by three different methods. The rate was 1.4×10-3 per sporidium per generation. The mutants formed two groups differing in reversion rates and were all homocysteineless.
The temperature coefficient (Q10) of the unstable strain was 1.3 and the activation energy for the mutation was 0.24ev. The ultraviolet dose-effect curve showed the peak and decline found in many other organisms.
From these results, it is concluded that strain T4001 has an unstable state of the genic substance at the homocysteine locus.
