668 
GENETICS: J. A. DETLEFSEN 
Proc. N. a. S. 
In addition to the Fi distribution coming from a single Pi pair, I also 
obtained a sample crossover value of the Fi coming from each of 44 other 
Pi females. I chose at random four Fi red, long double heterozygotes 
from each Pi pair. Each group of four Fi females was mated to white 
miniature Fi brothers. Thus we secured crossover values for 45 different 
Fi groups, each group coming from a single Pi pair. These Fi crossover 
values are put in the form of a frequency distribution in the fifth row of 
table 2. Here again we find the Fi values intermediate between the low 
stock and the original population. In no case was an Fi value as low as 
the mean or mode of the low parent nor as high as the mean or mode of the 
original population. 
Three distinct and separate F2 distributions were reared, coming from 
Pi pairs No. 2, 5 and 6. The value of each original Pi female, together 
with the crossover ratio of its Fi and F2 progeny, is given in table 3. 
TABLE 3 
The Data on Pi Pairs No. 2, 5, and 6, from Which the F-i Distributions WkrB 
Obtained 
Pl PAIR NO. 
CROSSOVER 
VALUE 
Fl CROSSOVER 
VALUE 
F2 CROSSOVER VALUE 
2 
21:382 - 
5.50 
29: 464 = 
6.25 
1060: 7812 = 13.57 
5 
7:193 = 
3.63 
72: 530 = 
13.59 
1477: 9001 = 16.41 
6 
6:178 = 
3.37 
251:1730 = 
14.51 
3161:21701 = 14.57 
The Fi distributions of table 2 show a wider range than the low parent or 
the Fl. In fact, the total F2 population with 148 pairs gives some females 
as low as the low parent and some as high as the original population. The 
mode is between the two stocks. It is clear that the results of these 
hybridization experiments bear the distinctive features of multiple factor 
inheritance with incomplete dominance ; for the Fi is intermediate and the 
F2 is likewise intermediate in its average but the F2 shows a conspicuous 
increase in range which easily overlaps both original Pi distributions. 
The increase in the standard deviation of each F2 population and of the 
total F2 distribution over that of the Fi or Pi puts these facts in concrete 
terms. Therefore, we can hardly escape the conclusion that multiple 
factors have a striking influence upon crossover values. In the frequency 
distributions of table 2, some variates will necessarily have little meaning 
because their crossover values are based upon small totals. I have 
thought it desirable to include every variate and thus withhold no data 
rather than include only such females as produced more than a fixed 
minimum of offspring. However, in order to show that the extremes 
in the F2 population are segregates, rather than fluctuations of sampling, 
I have given in table 4, detailed data on the highest and lowest 12 variates 
in the total F2 frequency distribution of table 2. The lowest 12 variates 
have values from 0%-9% and cover about the same range as the low 
