VARIABILITY IN LINKAGE OF CHARACTERS OF MAIZE 
23 
Evidence has been presented in preceding paragraphs showing 
the ratio of crossovers to be more variable than the Mendelian ratios. 
Five of the groups of ears presented in Table 15 afford an opportunity 
to make a similar comparison when there is no linkage. If the 
greater variability of the percentage of crossing over is due to 
linkage, this increased variability should disappear when there is 
no linkage. The comparisons are presented in Table 16. 
Table 16. — Comparison of the standard deviations (o-) of the percentage of 
waxy seeds with those of the crossover classes where no linkage is operative 
Standard deviations (per cent) 
Entry No. in Table 15— 
Per cent 
waxy seeds 
Per cent 
crossovers 
Crossovers- 
waxy 
DIE 
1 
2. 45±0. 26 
3. 56± . 37 
2. 30± . 18 
2.41± .26 
2. 14± . 21 
1. 81±0. 19 
3.58± .37 
3.81± .30 
3.14± .34 
2. 58± . 26 
-0. 64±0. 32 
. 02± . 52 
1. 51± . 35 
. 73± . 28 
• 44± .33 
2.0 
3 . 
.4 
4... _. 
4.3 
7 
2.6 
8 .. 
1.3 
Entry No. 4 is outstanding and indicates the existence of factors 
operating on certain zygotic combinations. It should be noted that 
this entry covers a group of self -pollinated ears, homozygous domi- 
nant for the linked factor C and heterozygous for the R aleurone 
factor. None of the other differences are significant, and the array 
of differences weighted by the reciprocal of the probable error 
squared is 0.47±0.27. 
It may be concluded that the differential death rate of zygotic 
combinations is not an important factor in the variability of the 
crossover classes. 
VARIABILITY OF RATE OF CROSSING OVER ALIKE IN PLANTS HETEROZYGOUS 
AND HOMOZYGOUS DOMINANT FOR R 
Four progenies are available in which half of the plants were 
heterozygous for the R aleurone factor, the other half being homo- 
zygous dominant for this factor. The factorial relations of these 
progenies are considered in detail on page 31 in connection with the 
rate of crossing over. These progenies provide an opportunity to 
determine whether the crossover rate is more variable when the R 
factor is heterozygous than when it is homozygous dominant. Eight 
comparisons are possible, involving measurements of male and fe- 
male gametes separately and combined, the latter being selfed ears. 
The data are shown in Table 17. 
The comparisons are made with <r 50 , since the mean rate of crossing 
over was not alike in the two factorial groups. Table 17 shows that 
in no single comparison is there a significantly greater variability 
for one factorial composition as compared with the other. Com- 
bining the differences between the o- 50 for the eight groupings shows 
that the plants heterozygous for R are on the average 0.53 ±0.24 per 
cent more variable than those homozygous dominant for this 
character. 
The actual difference in variability is somewhat greater than the 
calculations show, since among the back-crossed ears listed as R R 
