CHAPTER XXX 
NEO-MENDELIAN HEREDITY IN ANIMALS 
H. H. NEwMan 
Immediately after the announcement by De Vries in 1900 of the 
rediscovery of Mendel’s paper, zodlogists in Europe and in America 
began experiments in anima] breeding with the idea of discovering to 
what extent Mendel’s laws were applicable. It was soon found that 
the principles of unit characters, dominance, segregation, mono- 
hybrid, dihybrid, and trihybrid ratios were of practically universal 
application. A number of instances of Mendelian heredity in animals 
have already been presented in the preceding chapter and no more 
simple Mendelian cases need be described. For a considerable period 
the animal-breeders proceeded no farther in their analysis of the 
mechanism of heredity than Mendel had done so many years before. 
In time, however, new facts came to light that needed further analysis, 
and the older Mendelism was superseded by neo-Mendelism. This 
new phase in the study of heredity is in the forefront of interest today. 
Neo-Mendelian heredity in plants has already been discussed. It 
remains for us to present the data on some phases of neo-Mendelism 
in animals. 
ILLUSTRATIONS OF THE FACTOR HYPOTHESIS 
THE FACTORIAL ANALYSIS OF COLOR IN MICE 
Miss Durham, after extensive breeding experiments with numer- 
ous strains of differently colored mice, has been able to show that 
the appearance of a particular color in an individual mouse is depend- 
ent upon the presence or absence of several independently inherited 
factors, evidently represented by genes in as many different chromo- 
somes. It seems possible to classify these factors as follows: 
B=black pigment, which masks chocolate pigment 
b =absence of B, which gives chocolate 
I =intensity factor 
7 =absence of intensity, or dilution factor 
C =a complementary color factor acting with P 
P =a complementary pigment factor acting with C 
If either C or P are absent, albino mice result no matter what 
other color factors may be present. 
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