INDEPENDENT MENDELIAN INHERITANCE 85 
purple grains were obtained, but further breeding tests showed that 
these were simply heterozygous for purple coloration. A real exception 
must, however, be made for certain families which showed aleurone 
color segregation in the ratio 9 purple:7 white. Such results depend 
on the presence of two color factor differences and they will be explained 
later. The results in Ff, and F; for these plants of the genetic consti- 
tution WwSs are tabulated in Table XI. The expected results in each case 
are given in italics. 
Throughout the results in this table are substantially in agreement 
with theoretical requirements. The hypothesis has, however, been sub- 
jected to the further test of growing /’; populations. Table XII shows the 
kind of F's populations which are to be expected when I’) grains from 
this cross are planted. All these types of populations were secured. The 
case, therefore, provides an excellent illustration of the way in which a 
Mendelian experiment is carried out and of the excellent agreement 
with theory which is given in such experiments. 
TaBLE XII.—F; Ratios To BE EXPECTED FROM THE DIFFERENT GENOTYPES IN THE 
Cross WWss & wwSS 
| | ia 
| | Ratio in F's 
Phenotype | Genotype 
| Purple Purple | White White 
starchy | sweet | starchy | sweet 
SE). as. oan eee | | i fs 
Purple starchy...... WWSS | All | | 
WWsSs 3 | 1 | | 
WwssS' | Bee IN hare ane einen 1 
WwsSs 9 3 | 3 1 
Burplensweehaerscrsy  WAWISSS: | less cea naina ae | All 
Wwss ee aie eS SY |. |leuiaeteais Gone 1 
| 
White starchy..... wwss assesses Creal evo All 
wwss I esperar ss securtr | Reet sane eve tas 3 1 
White sweet....... TAs Nba eemeeee et seal (Sens Als ere wre sem lemony oats ra race All 
In the animal kingdom important work has been done in establishing 
Mendelian principles by the use of small animals, particularly mice, 
rats, guinea-pigs and rabbits. ° Such animals are particularly favorable 
for investigations in heredity because a large number of generations may 
be reared in a relatively short space of time. Castle has reported an 
excellent case of dihybridism in the guinea-pig. Rough coat is dominant 
to smooth and colored coat to the albino condition. When a smooth 
black is crossed with rough white the hybrids are rough black. In /’, 
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