VARIABILITY IN LINKAGE OF CHARACTERS OF MAIZE 9 
Table 3. — Summary of the published data- on linked seed characters in ma/ize 
showing variability in crossover rate 
Authority cited 
Sex of 
gametes 
Num- 
ber 
of 
Num- 
ber 
of 
Mean 
percent- 
age of 
Observed 
Coeffi- 
cient of 
O"50 
Cjo cor- 
rected 
for size 
1 
measured 
ears 
seeds 
cross- 
over 
tion 
of popu- 
lation 
Kempton (11), C-Wx . - 
Female and 
male. 
Female 
19 
9,065 
26. 60=fc0. 68 
4. 29=bO. 47 
16. 20=bl. 77 
4. 85=h0. 53 
5. 06=bO. 55 
Bregger (2), C-Wx 
9 
3,105 
26.70± .76 
3. 09=k . 49 
11. 40=bl. 80 
3. 49± . 56 
3.82=b .61 
Hutchison (9) , C-Wx.. 
do 
12 
6,704 
21. 71± . 55 
2. 62=h . 36 
12. 05±1. 65(3. 18± . 44 
3. 40=b . 47 
Emerson and Hutchi- 
/Male 
\Female 
19 
3,865 
38. 01± . 67 
4. 18=b . 46 
11. 00±1. 20 4. 30== . 47 
4. 48± . 49 
son (6), B-Lg. 
19 
4,257 
36. 58=b . 67 
4. 15=b . 45 
11. 35±1. 24 4. 31± . 47 
4. 49± .49 
Emerson and Hutchi- 
/Male.. 
\Female 
20 
5,640 
1.86=1= .08 
. 54± . 06 
28.80±3.07il.98± .21 
2. 06± . 22 
son (6), C-Sh. 
20 
10,548 
2. 98± . 13 
.83=fc .09 
27. 80±2. 96 2. 45=b . 26 2. 55=b . 27 
Similarly Gowen (7) has shown that in Drosophila, with environ- 
mental factors relatively constant and heritable differences reduced 
to a minimum, the percentage of crossing over is highly variable. 
Using the coefficient of variability Gowen concludes that double 
crossing over is more variable than single crossing over, but the 
propriety of using this measure of variability has been questioned 
(p. 6). If the observed stand ard de viation (a) of crossing over 
is compared with the expected, -y/pq/H, it is clear that double crossing 
over is less variable than single crossing over. Thus the o- of single 
crossing over exceeds the expected by 1.61 ±0.277, whereas the a- of 
double crossing over is but 0.005 ±0.048 in excess of that expected. 
It is evident, however, that single crossing over is highly variable 
and in excess of that expected, on the assumption that the popula- 
tions measured were random samples from a single population. 
Gowen's data are presented in Table 4. 
Table 4. — Standard deviations (a) of percentage of crossing over in the several 
regions of the third chromosome of Drosaphila melanogaster compared with 
the expected 
[Observed a from Gowen (7)] 
Region 
a 
■Jpq/H 
ff-Vpfl/H 
DIE 
Single crossing over: 
S e D' 
3. 81±0. 12 
6. 33± . 20 
8. 28± . 26 
9.65± .31 
2. 68± . 21 
3. 91=b . 12 
5. 92=b . 19 
7. 57=b . 24 
1. 68d= . 13 
2. 26± . 18 
3.03 
3.90 
4.46 
4.83 
1.61 
2.85 
3.83 
4.74 
2.21 
2.88 
3.01 
4.46 
1.04 
3.90 
0. 78±0. 12 
2.43± .20 
3. 82=b . 26 
4.82=h .31 
1. 07=b . 21 
1. 06=b . 12 
2. 09=b . 19 
2. 83=b . 24 
-. 53± . 13 
-. 62=fc . 18 
. 78± . 12 
1.64± .19 
1. 28± . 18 
1. 06=b . 15 
6.5 
S e S 8 
12.2 
S e e* 
14.7 
Sefo - 
15.6 
D'C a 
5.1 
B'Ss 
8.8 
D'e 3 
11.0 
B'To- 
11.8 
C u Ss... 
4.2 
S e H' . 
3.4 
Sae 3 . 
3. 79± . 12 
6. 10± . 19 
2. 32=b . 18 
4. 96=b . 15 
6.5 
S a r 
8.6 
H'e*. 
7.1 
e*r - 
7. 1 
Mean 
1. 608±. 277 
5.8 
1.03=b .03 
.95=b .03 
1.46=h .05 
.61± .02 
1.21=1= .04 
. 67=b . 02 
.99 
1.08 
1.16 
.75 
1.17 
.75 
Double crossing over: 
S a I>' and D'SS 
. 04=b .03 
-. 13=b .03 
. 30=b . 05 
-.14=fc .02 
.04=b .04 
-.08=fc .02 
1.3 
S e D' and S a e 3 
4,3 
SeD' and e 3 r 
6.0 
D'S e and S a e 3 
7.0 
D'S a and e e r 
1.0 
4.0 
. 005=t. 048 
.1 
19987°— 27- 
