Nos. 618-619] SHORTER ARTICLES AND DISCUSSION 359 



Case 



Fx Female Gametes 



o o o o 



OS 



e § ©•© 





foi 



s © © © 







© © © © 





o 



© © © © 







F% Zygotes : Phenopgpic Ratio io.-3.-3 



Negro- White Crosses" he found that the amount of black skin- 

 pigment in an individual is determined by two genes in each 

 parental gamete, and in measuring the intensity of black skin- 

 pigment in the members of a great many highly hybridized 

 families he found 5 definite maxima in the curve plotting the 

 distribution of individuals according to the per cent, of black 

 skin-pigment carried. Theoretically (unless genes "A" and 

 "B" are exactly equally potent in developing into a definite 

 per cent, of blackness showing in the unweathered skin) there 

 should have been 9 maxima in the above-described distribution 

 curve. Arbitrarily giving the genes the following potentiality 

 for somatic expression, "A" 16 per cent, "B" 19 per cent., 

 "a" 1 per cent., ££ b" 2 per cent, (which is not far from the 

 the facts of the case), the somatic frequencies and black skin- 

 color percentages would run as follows: One 70 per cent., two 

 54 per cent., one 36 per cent., two 55 per cent., four 38 per cent.. 



