EFFECT OF SELECTION ON CROSSOVER VALUES 
345 
In order to further test our foundation stock, the Fi offspring of 
9 25 (one of the eighty Pi 9 9 , and similar to 9 53) were 
tested en-masse and gave 1142: 3553 = 32.14 per cent. The Fi 
offspring of several other Fi 9 9 were mated en-masse and 
gave 830 : 2923 = 28.40 per cent. All of these facts indicate 
that our foundation stock was quite normal with respect to 
crossing over and gave crossover values of the same general 
magnitude as those ordinarily used in plotting maps of the sex 
chromosome. 
The main facts pertaining to series B are given in text figures 
1 and 2 and in tables 3 and 4. Table 3 was constructed in the 
31 33 35 
Generations 
Fig. 2 Series B, continued, low selection 
same way as table 1, with >he following exception: in series B, 
records of the en-masse matings of the offspring from several 
promising pairs were kept and the crossover values of all these 
are put in the form of a frequency distribution, but the itahcized 
frequency shows the position of the en-masse mating which was 
derived from the pair eventually selected to continue the experi- 
ment. The itahcized frequency in the distribution of the pairs 
likewise shows w^hat the value of the chosen pair was. The 
first three columns at the right of table 3 give the data for the 
total population in each generation. The average number of 
offspring per pair shows that the fertility was high and selection 
was based upon what seemed to be adequate numbers. The last 
column gives the number of crossovers total, and crossover value 
