No. 637] FIRST GENEBATION HYBRIDS 131 



number of dominant characters. Tliat is, populations of . 

 over 700 would have to be grown before there would be 

 an even chance of getting any individuals smaller than 

 those represented in these 12 classes. With ordinary 

 sized populations then the distribution would be fairly 

 represented by the distribution of the 12 largest classes. 



The distribution among these 12 classes would be as 

 follow^s : 



A distribution of this nature, with populations of ap- 

 proximately 500 individuals, conforms to the normal fre- 

 quency curve as closely as would be expected. The mode 

 departing from the mean by only 3/100 of a class. 



The theoretical distribution of an Fo population in- 

 volving 20 pairs of characters of equal weight with com- 

 plete dominance is shown in the accompanying diagram. 

 It will be noted that although the curve as a whole is 

 skew, the portion to the right of the class with 9 domi- 

 nant characters, which comprises 99.91 per cent, of the 

 area, is practically symmetrical. 



With 10 character pairs there would be 11 classes and 

 99.65 per cent, would fall in the 7 largest classes and in 

 this portion of the theoretical population the mode would 

 be separated from the mean by only 3/10 of a grade. 



Even should it bo possible to grow Fo populations suffi- 

 ciently Inru-c lo (Irtcct (l("])artures from a normal fre- 

 quency distril)iiti()n llwrr is yet another reason for ques- 

 tioning that a skew distribution should be expected, when 



