Lecture XXIX. 



267 



which if it were present would produce roundness. Similarly a 

 green pea owes its greenness to the absence of the determinant 

 which if it were present would change its colour to yellow. 



Mendel investigated the inheritance of a number of these allelo- 

 morphs, and he showed that like those, which I have just described, 

 they were each transmitted independently. In this way we come to 

 look at an individual as a mass of unit characters each represented 



errrvs 



RY 



Ova 



aY 



.ag 



FIG. 94. Diagram to illustrate the inheritance of two pairs of characters 

 (Roundness-angularity, Yellowness-greenness) in the F 2 generation. 

 The nature of the zygotes is represented by the figures in the sixteen 

 squares. The letters indicate the determinants contributed by the germ- 

 cells, those from the sperms being above in each case. The shape of 

 the zygote produced is shown by the outline (round or angular as the 

 case may be) : when yellow, it is marked with dots and when green, 

 with lines. 



by a determinant in the germ-plasm. And evidence has since been 

 adduced in favour of the view that the chromatin of the nucleus 

 contains these determinants. When both parents of an individual 

 contribute the determinant of a given character every gamete 

 produced by that individual will receive that determinant ; but 

 where only one parent contributes the determinant then only half 

 the gametes of the individual will receive and contain it. The 



