432 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
The ratio of 27, 9, 9, 9, 3, 3, 3, 1 Shows clearly that the three factors. 
independently segregate and are all three concerned in the determi- 
nation of the characters of the fur. A fourth factor, a pattern factor, 
is often present that further complicates thefactorialanalysis. Usually 
the self-color dominates the pattern, but certain special patterns are 
dominant over self-color. 
These two examples for animals are sufficient to illustrate the 
nature of Mendelian factors and their workings. Numerous other 
factors have been discovered. Castle, for example, found a factor 
associated with the occurrence of brown pigment in guinea pigs. 
Some rabbits have the pigment distributed evenly over the body; 
others have it in the eye only. These conditions are allelomorphic to 
each other, E (extension) being dominant over e (restriction to eyes). 
Inhibiting factors are distinguished, the presence of which prevents 
the appearance of a character represented in the germ plasm. Lethal 
factors result in the loss of something necessary for the life of the 
individual. Modifying factors change the expression of a character 
that depends on another gene. These and various other types of 
factors have been discovered by the large school of neo-Mendelians 
now so actively at work. 
