PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 363 



is homozygous ; the union of unlike gametes produces a heter- 

 ozygous animal. Conversely, a homozygous parent produces like 

 gametes, while a heterozygous parent forms equal numbers of 

 two classes of gametes, bearing respectively the two contrasting 

 characters. In our illustration, the pure bred black of the paren- 

 tal generation produced only "black" gametes ( if this strongly 

 abbreviated expression may be permitted), and the homozygous 

 white produced only "white" gametes. The only possible com- 

 bination of gametes was the union of black with white; hence 

 all the animals of the f^ generation were heterozygous. When 

 two of these heterozygous f, animals were bred together, each 

 produced "black" gametes and "white" gametes in equal numbers. 

 The totality of gametes produced by each animal may be repre- 

 sented by the expression lUack-j- White, conveniently abbreviated 

 to B-(-W ; and the resulting gamete comljinations may be rep- 

 resented by the product of the algebraic multiplication of B -j- W 

 by B -|- W, — namely BB -|- 2 BW -|- WW, which corresponds 

 to the observed proportion of i homozygous black (BB) :2 

 heterozygous blacks (2 BW ) :i homozygous white (WW). 

 This is the simplest possible type of Mendelian inheritance, in 

 which but one pair of contrasting characters is considered ; the 

 cases with two three . or more pairs of such characters may be 

 worked out on an algebraic basis. Aside from the confusion 

 caused by linkage, the observed results tally remarkably closely 

 with calculated ratios. 



Mendel's own work was done years before biology was in 

 position to look within the cell and raise the question as to the 

 material bearers of these hereditary characters. But when his 

 work was rediscovered, the researches of Oskar Hertwig, Stras- 

 burger, Kolliker, and Weismann had already turned the atten- 

 tion of the scientific world to the chromatin within the cell nucleus 

 as the probable carrier of hereditary characters. The breaking 

 up of the chromatin, at the period of cell division, into separate 

 bodies or chromosomes, of definite number and form in each 

 species, had already been discovered, as well as the significant 

 fact that the last two divisions in the development of egg and 

 sperm cells lead to the reduction of the chromosomes to one-half 



