November 22, 1912] 



SCIENCE 



719 



It is obvious on the other hand that half of 

 the females also contain one sex chromosome 

 that carries the lethal factor. They are saved 

 by the other sex chromosome, but they will 

 transmit the fatal dose to half of their sons 

 who die and to half of their daughters who 

 live. 



The same test has been made with another 

 sex-linked character, viz., miniature wings and 

 the same results obtained. If, however, the 

 lethal factor separates from the red-white fac- 

 tor (E — W) only once in 200 times it must be 

 near that factor, on my hypothesis of the 

 linear order of the factors in the chromo- 

 somes. If it does then we can calculate how 

 often the crossing over for the wing factor 

 should occur. In brief, we predicted the ratio 

 of long and miniature-winged males that are 

 expected in the back cross, i. e., how many 

 long-winged males would escape the fatal dose. 

 The prediction was verified. For example, 

 in F, there were obtained 



910 



it? 

 156 



243 



The number of cross-over males is 156, the 

 number expected for the total number (399) 

 of males is 133 ; this excess of long males is in 

 the direction which the known differences in 

 viability of long versus miiniature might pro- 

 duce. 



Similarly for the sex-linked factor for 

 "eosin eyes." This factor lies near to the 

 factor for red {B), hence in an experiment 

 similar to the one with white eyes, red-eyed 

 males should be rare. Up to the present time, 

 411 Fj eosin males have emerged and one red- 

 eyed male. The expectation is two red males 

 to 400 eosin males. 



T. H. Morgan 



COMPLETE LINKAGE IN THE SECOND CHROMOSOME 

 OF THE MALE OF DROSOPHILA 



It has been shown recently' that the non- 

 sex-linked factors that give black and wingless 

 flies are linked to each other. In the F„ gen- 

 eration (from Pj black winged by gray wing- 

 less) there were produced: 



' Morgan and Lynch, Biol. Bull., Vol. XXIII., 

 p. 174, August, 1912. 



GW BW Gw 



2,316 1,146 737 



1^0 black, wingless flies appeared which 

 seemed due to close linkage between the fac- 

 tors in question. Yet, when Fj gray, wingless 

 females were tested by breeding to black, 

 winged males quite a number of black flies 

 were obtained in the first generation (15 to 

 125). The explanation offered was that 

 " crossing-over " or breaking the linkage oc- 

 curred so rarely that in the production of the 

 F, generation no two wingless black gametes 

 had happened to meet. 



In order to test how often crossing-over oc- 

 curred, the experiment was repeated, but this 

 time the F^ females and males were tested for 

 cross-overs by mating them to black wingless 

 flies. Thus, black, winged females were mated 

 to gray, wingless males and gave Fj gray, 

 winged flies. The F, males were tested with 

 black wingless females and gave : 



BW 2 ^W c? Gw 2 Gw S 



514 478 355 366 



These results show that there has been no 

 crossing-over in the F^ heterozygous males. 



The converse cross was as follows: Gray, 

 winged females were bred to black, wingless 

 males and produced gray, winged males and 

 females. The F^ males were bred, as before, 

 to black, wingless females, and gave: 



GW $ GW c? Biu $ Bw S 



213 171 154 123 



Here again the combination that went into 

 the Fj male remained intact. 



Similar crosses in which the F^ females were 

 tested gave a different result : When F^ gray, 

 winged females (out of black, winged females 

 by gray, wingless males) were bred to black, 

 wingless males there were obtained: 

 BW2 BW^ GW2 GWS Bw2 BwJ Gw? Gw^ 

 696 717 305 273 180 127 606 511 



The converse cross, viz., F„ gray, winged fe- 

 males (out of gray, winged females by black, 

 wingless males) were bred to black, wingless 

 males and gave: 



BW2 BW^ GW2 GWS JBw2 Sw^ Gw^ GwS 

 222 191 1,018 928 668 657 202 146 



Adding the last two results together, it is 



