[Mutations hooded and nonagouti in the gray rat (Rattus norvegicus): effect of selection on behavior and photoperiod].

Selection of wild Norway rats for behavior conducted in different directions was shown to affect the rate of appearance of coat-color mutants. In the population selected for domestication (reduced aggressive-fearful behavior toward humans), almost all animals acquired the semirecessive mutation hooded (h). Selection for aggressiveness (enhanced aggressive-fearful response) was accompanied by an increase in the frequency of homozygotes for a recessive mutation nonagouti (a). In the population selected for aggressive behavior, seasonal variation in the rate of appearance of mutant animals was observed. Experiments on the maintenance of nonselected rats under artificial short-day conditions showed possible interaction between alleles Agouti (A) and nonagouti but exclusively in heterozygotes for hooded. This interaction may lead to the inactivation of the normal A allele in some AaHh heterozygotes and their transformation into aa homozygotes, which would resemble paramutation. Discussion of the results is focused on several issues: recent evidence on coat-color genes and their function, directional (as opposed to random) nature of appearing mutations, and the possibility of meiotic inheritance of genetic changes occurring in early development.