T W O DIAGRAMS
Three main points are dealt with in the following account: 1) The relative frequency of sex linked lethal factors in inbred stocks of Drosophila ampelophila in comparison with their occurrence in wild stocks. 2) The occurrence of new lethals and their linkage relations to other sex linked characters. 3) The demonstration that an extraordinary sex ratio was due to the occurrence of two different lethal factors each carried by one of the sex chtomosomes of the female that gave the ratio in question.
THE RELATIVE FREQUENCY OF LETHALS IN INBRED AND WILD STOCKS
A hundred virgin females of a stock of Drosophila which was caught at Falmouth, Mass., in the summer of 1912, were mated individually on November 29, 1912, with males of the same stock. The counts of the offspring from each bottle are shown in table 1.
A hundred virgin females from a stock that had been caught a t Falmouth, Mass., in the summer of 1911, were mated individually to males of the same stock early in January, 1913. The results are shown in table 3.
Numbers 13, 36, 38 and 47 of table 3 show a ratio of twice as many females as males while numbers 43, 53 and 67 are doubtful.
In order to determine whether the high ratios would reappear in later generations, virgin females from several of these cultures were mated to brothers.
Of the four sets of tests two (viz., 36 and 38) giveambiguous results, while numbers 13 and 47 give respectively 5 high to 9
The results are shown in table 4.