Nos. 618-619] SHORTER ARTICLES AND DISCUSSION 355 



FfFema/e Gametes 



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Fx Zygotes Phenotypic Ratios 



; Experiment.- 



The chemical experiments described in the accompanying fig- 

 ures parallel chemically what must happen to the F t genes in 

 their development into traits in the F„ somas in each case of a 

 modified somatic di-hybrid ratio. Each drawing represents a 

 2-inch wooden block 1\ inches square, with twenty-four |-inch 

 holes, \\ inches deep, suitable for holding test-tubes. The four 

 holes at the top hold test-tubes containing chemicals representing 

 the four types of ¥ x female gametes possible when di-hybrid ism 

 is being considered ; the four to the left perform the same service 

 for the four male gametes. The sixteen holes blocked off in the 

 square hold test-tubes for the sixteen types of zygotes resulting, 

 by the checker-board method, from all possible unions of the 

 four male and the four female gametes. X X represent the sub 

 stratum or the sum-totel of hereditary qualities other than the 

 traits under consideration. The lettering under each test-tube 

 circle is the genetic formula for the gamete, or zygote as the 



