Flower Color in Asy stasia gangetica — Kamemoto and Storey 
65 
TABLE 2 
The Ratio of Purple to Non-Purple Flowers in the F 2 Generation of Crosses between 
Purple and Non-Purple in Asystasia gangetica 
PROGENY 
OBSERVED 
CALCULATED 
CHI-SQUARE 
Purple 
Non-Purple 
Purple 
Non-Purple 
(12 X White) Selfed 
69 
16 
63.75 
21.25 
1.729 
<11 X White) Selfed 
74 
27 
75.75 
25.25 
.162 
( 1 X White) Selfed ...... 
9 
3 
9 
3 
.000 
< 6 X White) Selfed* 
84 
22 
79-5 
26.5 
1.019 
Total 
236 
68 
228.0 
76.0 
1.123 
Chi-square = 3.841 at 5 % level. 
* The cross 6 x White resulted in both purple and non-purple. The F a here is the result of selling the purple form. 
purple. The parental plants 1 , 11 , 12, and 
16 were determined to be homozygous for 
purple. Parental plant 6 was heterozygous for 
purple, segregating into 3 purple to 1 non- 
purple. When flowers homozygous for purple 
were crossed to white, the resulting Fi pro- 
genies were all purple. In the F 2 generation 
as shown in Table 2 the combined ratios were 
236 purple to 68 non-purple, a good 3:1 ratio, 
indicating that purple is dominant to non- 
purple. The symbol P has been assigned to 
the gene responsible for the production of 
purple color. Gene P when homozygous re- 
cessive will result in white flowers in the 
absence of other flower colors. 
It was observed in the first few crosses be- 
tween dark purple and non-purple forms that 
the flower color of the Fi generation was 
slightly less intense than the purple parent 
and that colors of the F 2 generation segre- 
gated into light and dark forms. This sug- 
gested the possibility of additive effects of 
gene P. Upon selfing pale purple parent 6, 
which was heterozygous for that factor, the 
offspring segregated into 3 purple to 1 non- 
purple, and among the purple progeny, both 
pale and dark forms appeared in the ratio of 
21 pale to 7 dark. Selfing a dark form resulted 
in all dark purple offspring, revealing the 
homozygous condition of that dark colored 
first selfed generation plant. Selfing a pale 
form, on the other hand, resulted in a segre- 
gating progeny of 3 purple to 1 non-purple 
again, which establishes the heterozygous na- 
ture of the pale purple first selfed generation 
plant. The ratio of light and dark forms ap- 
pearing among the purple forms was 31 to 11 
which is not a significant deviation from a 
2:1 ratio. 
In another case, a dark purple plant, Num- 
ber 12, was crossed to white, and resulted in 
light purple Fi plants. The F 2 generation 
segregated into 3 purple to 1 white and among 
the purple forms 49 were light purple and 20 
dark purple. This ratio fits a 2:1. Thus, it 
appears that the gene for purple is cumulative 
in its effect, that PP produces dark forms, 
Pp, light, and pp, whites. Such an additive 
effect of gene for the production of flower 
color is not new in plants. In Nicotiana hy- 
brids, Smith (1937) demonstrated that the 
heterozygous condition has a diluting effect. 
Also in Dahlias (Lawrence, 1931) the two 
genes, A and B, that determine anthocyanin 
color are cumulative in their effect. 
In addition to the cumulative action of gene 
P a modifying gene or genes may be operating 
to intensify or dilute the anthocyanin pig- 
ment, for not all flowers homozygous for P 
have the same intensity of pigment and not 
all segregating progenies can be subjected to 
simple genetic analysis. Further studies are 
necessary to clarify the inheritance of various 
intensities in coloration. 
