MEASUREMENT OF VARIABLE PROPERTIES 137 

 Parents Sxp 



Hybrids Fj DR 



Hybrids Fg . . b'-+ . . . 2 DR+ . . . R^ 



Hybrids F3 



DK . .D^ + 2DR + R^ ...R^ 



§ 105.— ELEVENTH EXAMPLE (continued) .—In a second 

 experiment MENDEL crossed a variety or subspecies (pea) a 

 with round seeds {D) and yellow albumen (d) with a variety b 

 with wrinkled seeds [R) and green albumen (r). Here each egg 

 (or seed) of the Fj generation is made by the union of a germ cell 

 (taken from a) containing two factors D and d and a germ cell 

 taken from b and containing the factors R and r. One 

 possibility exists : the production of a seed DdRr (D and d 

 dominant ; R and r recessive). 



From the Fj seeds DdRr plants are raised which give birth to 

 four sorts of germ cells. With regard to the pair of primordia 

 D, R, the germ cells are segregated into two groups D and R, 

 which are in equal numbers among the ^ and among the ? — 

 let us suppose 250 D $ , 250 D ? , 250 R $ , 250 R $ . With 

 regard to the pair d and r, a similar segregation occurs, inde- 

 pendently of the first one, in such a way that each of the four 

 above groups is segregated into two equally numerous groups. 

 Eight groups of germ cells are obtained — viz. 



125 Dd $, 12s Dr $, 125 Rd $ , 125 Rr $ 

 125 Dd $ , 125 Z)r ? , 125 Rd ¥ , 125 Rr ? 



The germ cells of any given $ group being distributed at 

 random among the four groups of $ germ cells, since the latter 

 groups are equally numerous, the frequency of each of the four 

 possible sorts of compound events is \. The $ groups being 

 four in number and equally numerous, the frequency of each 

 sort of $ germ cells is J. Each of these 4 groups giving 4 

 compound events, the totd number of possible compound events 

 (seeds) is 16, the frequency of each being \ x ^ = ^ — viz. 



