148 
The various homozygous combinations of these two factors give four 
GENETICS IN RELATION TO AGRICULTURE 
primary races which breed true as follows: 
By hybridizing these races four heterozygous forms may be produced 
which are of the colors given below: 
YYRR = crimson. 
YYrr_ = yellow. 
yyRR = white. 
yyrr = white. 
YYRR (crimson) X YYrr (yellow) gives Y¥ kr = orange red. 
YYRR (crimson) X yyRR (white) gives YyRR = magenta. 
YYRR (crimson) X yyrr (white) gives YyRr = magenta-rose. 
YYrr (yellow) X yyrr (white) gives Yyrr = pale yellow. 
ou YR Yr yR yr 
9 YYRR | YYRr | YyRR YyRr 
YR Crimson Orange red Magenta Magenta rose 
Vira Yioverr | YyRr Yyrr 
Yr Orange red Yellow | Magenta rose Pale yellow 
YyRR YyRr yyRR yyRr 
yk Magenta Magenta rose White White 
Yykr Yyrr yyRr yyrr 
yr | Magenta rose Pale yellow White White 
Fia. 68.—Checkerboard analysis of the progeny of a magenta-rose Mirabilis of the genetic 
constitution YyRr. 
We thus have seven distinct color classes as a result of various com- 
binations of two pairs of color factors. 
Moreover, this species gives a very good example of the diversity 
which may be obtained in an fF, population. Thus Miss Marryat 
has shown that when magenta-rose, YyRr, is selfed, the progeny fulfil 
the conditions indicated by the accompanying checkerboard analysis 
in Fig. 68. 
"Tanne XXIX.—F, Puenorypys anpD F; Puwnorypic Ratios DERIVED FROM 
THE OriGINAL Cross, Crimson, YYRR & Wuire, yyrr 
Number of Number of 
Color of parent 
plants selfed | offspring Color of offspring 
ello Wieeare ieeiinnae 2 | 26 All yellow. 
Grimson. .)7.523-5 5% 2 23 All crimson. 
Orange red......... 3 61 17 crimson : 31 orange red : 15 white. 
Magenta secede a 4 64 18 crimson : 32 magenta : 14 white. 
Pale yellow....... .,| 3 46 9 yellow : 25 pale yellow : 12 white. 
Magenta-rose....... 5 70 5 crimson : 9 magenta : 6 orange red: 
19 magenta-rose : 3 yellow: 7 pale 
yellow : 21 white. 
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