On the relationship between the frequency of two types of lethal-mutation and x-ray doses in Drosophila.

The dose-frequency relationship for each of 2 types of lethal mutations, fractional- and whole-lethal, was obtained using X-rays on Drosophila melanogaster. The results show that fractional-lethal mutations are induced by X-rays, and also that the proportion of fractional-lethal mutations in the total of mutations tends to decrease with increasing doses, namely, 61% at o R, 47% at 500 R, 37% at 1000 R and 20% at 2000 R. The same tendency is observed with visible mutations. In order to consider the problems related to the above results, the relationship between the true frequency and the observed frequency of the induced lethal mutations is discussed, taking into consideration the existence of the ostensible whole-lethal and the ostensible normal.