On the varying dominance of certain white breeds uf the silk-worm, etc. 270 



As we expected, he obtained two kinds of F^ broods, one all 

 yellow and the other a mixture of yellow and white. On comparing 

 these figures with ours, we at once see that the former is the result 

 of the recessive white mating and the latter the heterozygous white 

 of which we gave a minute description in the former pages. There 

 are, however, certain forms required by the calciolation which are 

 not represented in his figures. For instance, an expected all yellow 

 F2 brood in the recessive mating and two kinds of i w : i Y Fg broods 

 in the heterozygous are not found in his figures. A few cases of 

 similar nature were also found in F3 of the heterozygous matings. 



II. White females doubly mated with white and 

 yellow males. 



In these matings, for the same reason before stated, we expect 

 to have nine gametic combinations in Fj: 



A. Dominant white females doubly mated with the mixed white 

 males and yellow males. 



I WW + YY = WW 4- WY = all white. 

 9 W^V ■ d ] WW' + YY = Ww + WY = all white. 



I Ww + YY = (WW + Ww) + WY = all white. 



B. Recessive white females doubly mated with white and 

 yellow males. 



I WW 4- YY = Ww + wY = I W : I Y. 

 9 WW >; rj < WW -j- YY = WW -\- wY = i W : i Y. 



I Ww + YY = (Ww 4- WW) -f- wY = I W : I Y. 



C. Heterozygous white females (Ww) doubly mated with white 

 and yellow males. 



I WW + YY = (WW + Ww) + (WY + wY) = 3 W : i Y. 

 9 Ww X <3 I WW + YY = (Ww 4- WW) 4- (WY 4- wY) = 3 W : i Y. 



I vVw 4- YY = (WW 4- 2 Ww 4- WW) 4- (WY 4- wY) = 3 W : i Y. 



Thus dominant white females doubly mated with white and 

 yellow males give three kinds of all white F^ broods, recessive white 

 females three kinds of i w : i Y broods and heterozygous white females 

 also three kinds of 3W:iY broods. Each of these broods paired 

 inter se will give different kinds of Fo broods. Let us now see the 

 posterity of each brood. 



A. Posterity of Fj white produced by the dominant white females 

 above referredto. 



In this series, there are three kinds of Fx; namely, a) a 

 mixture of homozygous (ww) and heterozygous dominant (wY) whites, 



