Allelism of Second Chromosome Lethals in D. Melanogaster

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Abstract
Flies of the Oregon-R strain with lethal-free second chromosomes were allowed oviposit in plastic cups, which were then placed around a 500-mg. radium bomb. The emerging flies were thus exposed to a constant dose of gamma rays of approx. 5r per hour. After 18 days (2175r) males were removed and mated individually to Cy L/Pm females. The F1 Cy L/+ males were mated singly with Cy L/Pm females, and the resulting Cy L/+ males and females of each culture were interbred to determine the lethal mutation rate by the absence of wild-type flies in the F3. The frequency of lethal chromosomes was 12.09 [plus or minus]0.53% and the freq. of lethal genes, according to the Poisson distr., 12.89[plus or minus]0.60%. In intercrosses of Cy L/+ flies from 100 lethal cultures of independent origin, 14 of the 4950 possible matings failed to produce wild-type flies, so that the frequency of allelism between treated chromosomes was 0.28%. The minimum no. of loci capable of mutating to lethality was calculated to be 400, with limits of 234-718.