PHENOMENA OF INHERITANCE 255 



of Mendelian inheritance are more simply 

 stated in terms of presence or absence of 

 single characters than in terms of contrasting 

 characters. But it is by no means certain that 

 recessive characters are due to the absence of 

 factors for dominant characters; there are 

 some genetical and many philosophical objec- 

 tions to such a view, which leads logically to 

 some strange conclusions, such as Bateson's 

 speculations on evolution (p. 404). 



When both gametes carry similar positive 

 factors the zygote has a "double dose" of such 

 factors and is said to be duplex; when only one 

 of the gametes carries such a factor the zygote 

 has a "single dose" and is simplex, when 

 neither gamete carries a positive factor or fac- 

 tors, the zygote receives only negative factors 

 and is said to be nullipleoc. Thus the union of 

 gametes AB (?) and AB (<?) yields zygote 

 A ABB, which is duplex in constitution; 

 gametes Ah (?) and aB (<?) yield zygote 

 AaBb, which is simplex; gametes ab (?) and 

 ab (<?) yield zygote aabb, which is nulliplex. 



In some instances a character comes to full 

 expression only when it is derived from both 



