THE OCCURRENCE OF LETHAL FACTORS IN INBRED 

 AND WILD STOCKS OF DROSOPHILA 



MARY B. STARK' 



(From the Zoological Laboratory, Columbia University) 



TWO 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 occur- 

 rence 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 chromosomes 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, w^-ith 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 

 at Falmouth, Mass., in the summer of 1911, were mated indi- 

 vidually 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. The results are shown in table 4. 



Of the four sets of tests two (viz., 36 and 38) give ambiguous 

 results, while numbers 13 and 47 give respectively 5 high to 9 



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THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 19, NO. 4 



