332 GENETICS: S. WRIGHT Proc. N. A. S. 
able explanation, however, is that dominance is lacking and this view will 
be adopted provisionally. 
With this assumption, our three equations for determining the values 
of K^, and are as follows in the two stocks under consideration. 
EXP. B 
PAM. 35 
(5) -h -\- = I 
(10) from (6), rpo ^ 'hh^ = 
0.211 
0.014 
(11) from (7), roo^ = + = 
0.214 
0.069 
= 
0.422 
0.028 
0.003 
0.055 
0.575 
0.917 
1.000 
1.000 
Thus in the control stock, variations in pattern are determined about 
42% by heredity, and 58% by irregularity in development, leaving nothing 
for tangible environmental factors. In the inbred family the correspond- 
ing figures are 3% for heredity, 5% for tangible environment and 92% 
for irregularity in development. We can find the mean squared deviation 
due to each kind of factor by applying these percentages to the total squared 
standard deviation of each stock. (Equation 3 and table 1.) 
CONTROI, (b) 
IMBRED (35) 
Heredity, o-q ^ 
0.271 
0.010 
Tangible environment, (tq 
0.002 
0.020 
Development, ctq ^ 
0.370 
0.334 
Total, <TQ 
0.643 
0.364 
If these results had been obtained in the control stock before the inbreed- 
ing commenced, the extent to which the variability of the stock should be 
reduced by inbreeding could have been predicted, assuming dominance 
to be lacking. Inbreeding automatically renders all Mendelian factors 
homozygous and, therefore, eliminates all genetic variability. There is 
no reason for supposing that variability due to environmental or onto- 
genetic causes would be affected. The sum of the mean square deviations 
due to the latter causes is 0.372 in the control stock. This, then, is the 
mean square deviation to be expected after prolonged inbreeding, while 
its square root, 0.610, is the expected standard deviation. The actual 
figures in the inbred family, 0.364 for the mean square deviation, 0.603 
for the standard deviation, are an even better check than could reasonably 
be expected on the accuracy of the assumptions on which the degrees of 
determination were calculated. 
