82 GENETICS IN RELATION TO AGRICULTURE 
constitution is WwSs, and it contains two pairs of factor contrasts. 
Such a hybrid produces gametes representing all possible combinations 
containing one member of each pair of factors. The gametes, therefore, 
will be produced in the combinations and proportions 
1 WS:1 Ws:1 wS:1 ws. 
This series of gametes will be represented in both the pollen grains and 
ovules, so that if each kind of ovule has an equal chance of being fertil- 
ized by any one of the four kinds of pollen grains the following combina- 
tions will result. 
TaBLp X.—ComBINATIONS OF FacToRS AND CHARACTERS RESULTING FROM 
SELF-FERTILIZATION OF A PURPLE STARCHY CORN OF THE 
Composition Ww/s. 
WS ovule and WS pollen grain gives WWSS, purple starchy 
WS ovule and Ws pollen grain gives WWSs, purple starchy 
WS ovule and wS pollen grain gives WwSS, purple starchy 
WS ovule and ws pollen grain gives WwSs, purple starchy 
Ws ovule and WS pollen grain gives WWSs, purple starchy 
Ws ovule and Ws pollen grain gives WWss, purple sweet 
Ws ovule and wS pollen grain gives WwSs, purple starchy 
Ws ovule and ws pollen grain gives Wwss, purple sweet 
wS ovule and WS pollen grain gives WwSS, purple starchy 
wS ovule and Ws pollen grain gives WwSs, purple starchy 
wS ovule and wS pollen grain gives wwSS, white starchy 
wsS ovule and ws pollen grain gives wwSs, | white starchy 
ws ovule and WS pollen grain gives WwSs, purple starchy 
ws ovule and Ws pollen grain gives Wwss, purple sweet 
ws ovule and wS pollen grain gives wwSs, white starchy 
ws ovule and ws pollen grain gives wwss, white sweet 
When the fF, grains are classified according to their phenotype, 
they are distributed as follows: 
9 grains with purple aleurone and starchy endosperm 
3 grains with purple aleurone and sweet endosperm 
3 grains with white aleurone and starchy endosperm 
1 grain with white aleurone and sweet endosperm 
Just as the 3:1 ratio is typical for the monohybrid when one of the 
contrasted characters is dominant, so the 9:3:3:1 ratio is charac- 
teristic of dihybrids when one member of each pair of characters is domi- 
9 
nant. This ratio is clearly derivable from the simple 3:1 ratio, for 
considering first aleurone color, the segregation is in the ratio 3 purple: 1 
Digitized by Microsoft® 
