20 
BULLETIN 1468, U. S. DEPARTMENT OF AGRICULTURE 
tion of the crossover rate being more variable in the early than in 
the late gametes. The difference is 2.37±1.99, which, of course, is 
not statistically significant. 
CROSSOVER RATIO MORE VARIABLE THAN MENDELIAN RATIOS 
It has been shown that crossing over, as measured by the percent- 
age of individuals in the crossover classes, has a variability not to 
be ascribed to errors of random sampling. 
If this variability results from irregularities in the mechanism 
of crossing over or from a differential death rate of crossover 
gametes or zygotes, the percentage of crossing over should be more 
variable than the Mendelian ratios expressed as percentages. 
/ , 
Table 14. — Comparison of the variability of the crossover rate with that of 
the percentage of the Mendelian character waxy endosperm in female and 
male gametes 
Progeny 
Female gametes: 
Dh 416L3L1C1L1L22. 
Dh 416L3L1C1L1L1L23 
Dh 416L3L1C1L1L2L23 
Dh 416L3L1C1L1L3L23 
Dh 416L3L1C3L21 
Dh 416L3L1C3L1L22 
Dh 416L3L1C5L21 
Dh 416L3L1C5L4L23 
Dh 416L3L1C5L4L1L24 
Dh 416L3L1C5L3L1R23.— 
Dh 416L3L1C5L3L2R23 
Dh 417L1L2L1L21 
Dh 417L1L2L1L2L23 
Male gametes: 
Dh 416L3L1C1L1L22.... 
• Dh416L3LlClLlLlL23. 
Dh 416L3L1C1L1L2L23. 
Dh 416L3L1C1L1L3L23. 
Dh 416L3L1C3L21 
Dh 416L3L1C3L1L22— . 
Dh 416L3L1C5L21 
Dh 416L3L1C5L4L23.... 
Dh 416L3L1C5L4L1L24. 
Dh 416L3L1C5L3L1R23. 
Dh 416L3L1C5L3L2R23. 
Dh 417L1L2L1L21 
Dh 417L1L2L1L2L23.... 
Mean... , 
Combined sexes. 
Num 
of 
ears 
Num- 
ber of 
seeds 
1,919 
3,400 
3,064 
2,933 
2,331 
3,296 
4,068 
3,523 
7,336 
24,627 
5,284 
4,995 
4,122 
1,885 
2,104 
2,722 
1,387 
4,100 
2,266 
7,352 
3,661 
6,300 
27, 517 
3,683 
4,693 
3,757 
Crossover 
Per cent 
24.75 
25.80 
31.41 
31.00 
27.16 
28.25 
32.57 
39.40 
35.50 
20.47 
22.16 
20.62 
25.10 
20.53 
24.50 
32. 36 
30.50 
23.20 
22.11 
29.65 
35.80 
37.60 
18.07 
27.42 
16.71 
29.30 
O"60 
3. 43±0. 82 
5. 31± . 96 
7. 32±1. 23 
4. 86± . 88 
41±1. 37 
30± . 92 
88±1. 68 
29± . 59 
3.04± 
6.49± 
6.82± 
5.95± 
4.81i 
2. 53±0. i 
7. 67±1. ; 
52±1. 03 
37±1. 15 
13±1. 09 
38±1. 14 
81±2. 10 
32± . 42 
02± . 35 
5. 22=fc . 36 
4. 46± . 64 
3. 63zfc . 48 
5. 10± . 95 
Waxy 
Per cent 
49.4 
49.6 
51.2 
48.5 
50.1 
50.0 
48.7 
49.8 
49.2 
50.3 
49.4 
49.9 
51.3 
51.1 
49.8 
49.6 
49.0 
56.0 
54.1 
48.5 
47.7 
46.7 
48.1 
46.3 
50.2 
49.3 
2. 87±0. 
1.44=b . 
2. 59± . 
1. 66± . 
1. 29± . 
1. 88± . 40 
4. 52± . 82 
2. 11± . 24 
2. 34± . 16 
1. 68± . 24 
2. 80=k . 37 
3. 51=L . 46 
2. 35±0. 56 
1. 70± . 31 
2. 93± . 49 
2. 50zh . 45 
4. 33± . 92 
1. 75=fc . 37 
1. 49± . 32 
2. 70± . 49 
3. 44± . 40 
3. 17± . 22 
3. 62± . 52 
2. 88± . 38 
3. 07± . 41 
Difference 
O"50C0 — vwx) 
0. 56±1. 07 
3. 87± . 99 
4. 73±1. 31 
3. 20± . 93 
5. 12±1. 40 
3. 33± . 94 
6. 00±1. 73 
-1.23±1.01 
. 93± . 43 
4. 15± . 47 
5. 16±1. 01 
3. 15± . 87 
1. 30± . 79 
2. 60± . 34 
0. 18±0. 82 
5. 87±1. 39 
3. 59±1. 14 
3. 87=bl. 23 
. 80±1. 43 
3. 63±1. 20 
8. 32±2. 12 
-. 38± . 64 
- 42±.53. 
2. 05± . 42 
. 84± . 82 
. 75± . 61 
2. 03±1. 03 
1. 28± . 31 
1. 93± . 24 
There may be some question as to the propriety of comparing the 
standard deviations of crossover percentages with those of the per- 
centages of the Mendelian characters, since the deviations of the 
latter are strictly limited. Thus, if the percentages of the Mendelian 
characters depart widely from the expected, a gametic composition 
that will explain the observed ratios is hypothecated. This is espe- 
cially true in dealing with aleurone color where six factors are 
recognized. No such procedure is possible in the present stage of 
our knowledge of linkage relations, and if the crossover percentages 
