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THE AMEBIC AN NATURALIST [Vol. XLIX 



producing spermatozoon, which carries therefore an X 

 chromosome received from the mother of the F l males 

 and bears her character. In the present case the male 

 carries the chromosome bearing red abnormal. 



Since red and abnormal dominate, all the F 2 females 

 should be red abnormal, except in so far as the conditions 

 suppress the abnormal and induce the normal type. The 

 experiment. Table I, shows that very few normal females 

 were present. 



Four classes of males are expected — the large class of 

 non-cross-overs RAb and AVX, and two small classes of 

 cross-overs EN and WAb. It will be observed (Table I) 

 that the linkage between R and Ah is very strong, since 

 nearly all of the males are either RAb (647) or NW (664). 

 Only a few crossovers RX (25) and WAb (13) males 

 were present. The percentage of crossing over is 1.97 

 per cent, when the abnormal males alone are used for 

 calculation. 



In the reciprocal cross the RAb male was mated to 

 WN female, and gave in F 1 RAb females and WN males. 

 The F 2 record is given in Table II. 



Since the same two pairs of factors enter as before, 

 the same chromosome diagram will suffice for the gametes 

 of the F t female. The F, male is, however, a double re- 

 cessive (WN) ; in consequence four classes of females 

 are expected as well as of males. The gametes of the 

 F t female are as before the following: 



