852 RADIATION BIOLOGY 



control males. In later publications Hertwig (1942a, b, 1944, 1949, 1951) 

 describes two recessive visibles, shaker-syndactyly and "Kreisler," that 

 were recovered from presterile-period matings. These are first described 

 as having come from males exposed to 1000 r and would, therefore, appear 

 to be additional to the visibles from presterile-period matings reported in 

 1939 which were recorded as coming from males treated with 800 r. 

 There seems to be some confusion over doses, however, because shaker- 

 syndactyly is later described as having come from a male exposed to 

 1500 r, and the dose given to the male that produced anemia in descend- 

 ants of a poststerile-period mating is reported as 1500 r in one place and 

 1000 r in another. Combining offspring of presterile- and poststerile- 

 period matings, taking the total number of visibles as from five to seven, 

 assuming that the total number of offspring tested was the 118 reported in 

 the 1941 publication, and using the weighted mean dose of that portion of 

 the data for which the doses are recorded, the induced mutation rate to 

 recessive visibles is from 4.1 to 5.7 X 10~ 5 per r. All of the four muta- 

 tions that have been described in detail fall on the borderline between 

 semilethals and subvitals, and only one has shown any fertility. Taking 

 the number of lethals as from four to six in 118 tested offspring, assuming 

 the mean dose used above, and subtracting the control rate, the induced 

 mutation rate to lethals is from 0.59 to 2.2 X 10 -5 per r. Since visibles 

 with not easily recognizable effects were probably not detected, and since 

 lethals are difficult to detect with the methods available in mammals, the 

 above rates are probably much below the over-all mutation rates to 

 visibles and lethals. 



In the investigation by Russell (1951), which has already been men- 

 tioned in the section on dominant visible mutations, wild-type male mice 

 were exposed to a single whole-body dose of 600 r of X rays and, after 

 their period of temporary sterility, mated to a stock homozygous for 

 seven autosomal recessive visible genes. Control, unexposed, males were 

 also mated to the test stock. The offspring were observed for mutations 

 at the seven specific loci. Presumed mutants were saved and breeding 

 tests made to determine the allelism and the effect of the mutations in 

 homozygous condition. Thus, the method used detects mutations to 

 recessives, including those with lethal effect when homozygous, at a 

 limited number of specific loci. The mutations obtained at each locus 

 are listed in Table 12-10. Table 12-10 includes the results from a pilot 

 experiment conducted mainly to determine the relation of dose to survival 

 and productivity of the exposed animals. Various doses were used in 

 the pilot experiment and detailed tabulation with regard to this and other 

 variables was postponed until completion of that experiment. 



Taking the total number of mutations in the irradiated group in the 

 main experiment as fifty-three and subtracting the control from the 

 experimental rate, the mean induced mutation rate, in spermatogonia, for 



