EFFECT OF TEMPERATURE ON CROSSING OVER 
193 
An examination of tables 2 and 3 and of figure 2 discloses an 
interesting situation in the third chromosome. It seems clear 
from table 2 that high temperature causes a definite increase in 
crossing over between sepia and Dichete and a very marked one 
between Dichete and spineless, but little if any change in the 
remainder of the chromosome. Table 3 and a comparison of the 
full and dotted lines in figure 2 bring out this fact even more 
definitely, but without separating sepia and spineless by the 
40 
38- 
36 
34 
1 
1 
1 
1 
1 
seplaT-splneless 
32 
30 
1 
28 J 
1 
26 
1 

— r 
" 
24 
15 
^^- !,-_ 
Spineless-sooty 
I 
13 
-1' 
11 
— 1 
1 
n 
9 
28' 
26- 
24 
22. 
1 
1 
sooty-ro'jgh 
--- 
1 
20 
J 
1 
IB- 
1 
IS 
". 1 
4 
7 
10 
1 
3 16 
1 
9 26 
Fig. 2 Curves of crossing over for different regions of chromosome III. The 
control values are the solid lines; the values for the heat-treated lines are dotted. 
The abscissas are days after mating, the ordinates percentages of crossing over. 
Dichete mctor. The dotted line for the sepia spineless region 
begins at a point about 6 units higher than the control, rises 
to a difference of 13 units, and drops sharply to about the 
same point at about the tenth day. This indicates, as in the 
second chromosome, that the eggs which go through the critical 
period at the high temperature show a much increased crossover 
ratio, but that those which pass through that period subsequently 
(i.e., after the females are replaced at the control temperature) 
are not affected. The dotted Une for the spineless sooty region, 
on the other hand, shows no significant difference. That for 
