June 7 ,1924 A Genetic and Cytological Study of Wheat Hybrids 1023 
Table III .—Marquis X Alaska — F 2 behavior as indicated by F% segregation; 
showing the number of F s families which breed true for the alternative characters^ 
and the number which show segregation 
Characters studied 
Behavior of Fa families 
n 
Awning... 
Awnless. 
28 
Segregating. 
51 
Awned. 
31 
Actual number.... 
110 
Theoretical for 3:1 ratio...... 
27.5 
55 
27.5 
Awn color.......,. 
Yellow. 
Segregating. 
66 
Black. 
18 
Actual number..... 
26 
110 
Theoretical for 3:1 ratio.... 
. 27.5 
55 
27.5 
Grain texture....... 
Hard. 
Segregating. 
80 
Soft. 
8 
Actual number... 
10 
98 
Spike shape......... 
Normal. 
Segregating. 
89 
Branched. 
Actual number.. ..... 
17 
4 
110 
Type keel.... .. 
Vulgare. 
13 
Segregating. 
96 
■Durum- 
Actual number....... 
1 
. 110 
Grain color..... 
Red. 
Segregating. 
56 
White. 
Actual number..... 
32 
6 
94. 
If no segregation occurred in seven or eight or more F 3 individuals of a certain 
family the F 2 parent was considered homozygous for the character involved 
(assuming a single factor to be involved). In this way the different F 2 individuals, 
could be classed as homozygous for one character or the other or heterozygous, 
as indicated by F 3 segregation. 
When all F 3 plants of a given family had an awn length of less than 3 cm. 
the F 2 was considered homozygous for the awnless condition. It was found 
that all of the F 2 individuals in the first two classes bred true for awnless or 
segregated into awned or awnless in the F 3 . Some of the individuals are classed 
as having awns from 4 to 10 cm. long on the tips in the F 2 bred true for awns 
in F 3 , while a few of them segregated into awned and awnless. All of the F 2 
individuals which had awns 4 cm. and longer distributed the entire length of 
the spike bred true for the awned condition in F 3 . The segregation of the awned 
condition as shown in Table III clearly indicates a simple one-factor difference 
for so-called awnless and awned segregates in F 2 . This behavior is in accord 
with results found in varietal crosses (4, 7, 5, 9 ). 
Although it is practically impossible to accurately classify awn color in F 2 , 
due to the effect of environmental factors, it is comparatively easy to classify 
the F 2 segregates based on F 3 behavior. The effect of environmental factors is 
undoubtedly responsible for the excess of individuals classified as segregating.. 
No doubt a certain number of these individuals are genetically black, but climatic 
conditions in some way inhibit the black color from appearing in certain indi¬ 
viduals, so the F 3 family was classed as segregating into black and yellow. 
There is, however, little question but that here again a simple factor for black 
versus yellow or brown is involved. 
A great majority of F 3 families showed segregation for grain texture. Only 
10 individuals were homozygous for hard grain and 8 homozygous for soft grain. 
There is, apparently, no simple Mendeliah factor difference involved in this case. 
Individuals were also classified according to shape of spike, whether normal or 
branched. In the F 3 there were several individuals which were quite similar 
to the Alaska, at least in the morphological appearance of the spike. In F 2 five, 
segregates out of 152 were classed as branched while 48 were classed as partially 
branched, that is, showed some tendency of branching of a few spikelets. It is 
evident, then, that the normal condition is partially dominant over the branched? 
condition. All of the completely branched individuals in F 2 which resembled, 
the Alaska parent to some extent, bred true in F 3 . There is in this case no, 
indication of simple Mendelian segregation. 
