272 



AN INTRODUCTION TO MODERN GENETICS 



fully investigated the local races of Lymatria dispar (the Gipsy moth) 

 from various parts of Europe and Asia. The data are most complete 

 about the races from the islands of Japan. One characteristic which 

 distinguishes the different races is the strength of the sex factors (p. 216). 

 The male factor which is carried on the X chromosome gives rise to a 



MANCHURIA 



STRONG 



LUS 



H -h NEUTRAL MINUS 



Fig. 123. Distribution of Sex Races of Lymantria. — Notice the fairly orderly 

 distribution, the strength increasing from west to east and south to north. The 

 only exception is the weak race on the northern island of Hokkaido; but the 

 Hokkaido race differs from the others in several ways; there is a considerable 

 change in the whole fauna at the strait between Hokkaido and the main island; 

 and this strait was formed before the main island was separated from the mainland. 



series of races which may be called strong, weak, or intermediate, for 

 which Goldschmidt postulates at least eight allelomorphic genes; the 

 strengths cannot be due to combinations of factors at different loci on 

 the X since no crossing-over and recombination occurs. The female 

 factors, whose strength in each race is necessarily balanced against that 

 of the male factor, is carried in the cytoplasm. 



The rather orderly geographical distribution of the sex races indi- 

 cates that the strength of the sex factor may be in some w^ay adaptive, 

 but its exact significance for the life of the animal is not understood. 

 Goldschmidt has, however, also investigated some clearly adaptative 



