Professor Mukai was my postdoctoral associate for more than two years, from June 1965 through July 1967. In this article, I discuss mainly the work done during that period.
Mukai's best known accomplishment was to demonstrate that the total deleterious mutation rate is considerably higher than was previously thought, due to the very high rate of mutation of viability-depressing polygenes. These are at least 25 times as frequent as lethals. These experiments, utilizing a mutation-accumulation scheme, were clever in design, meticulous in execution, and heroic in scope. In related experiments he showed that the typical viability-reducing mutation is deleterious in the heterozygous as well as homozygous state. From the viability experiments he was able to infer that there is strong heterozygous selection for fitness, comparable to that for lethals.
All of Mukai's research was characterized by a willingness to undertake problems that involved enormous numbers of Drosophilae and many hours of work. His ability to plan such experiments and to see that they were carried out carefully was a rare gift, one that the genetics community will sorely miss.