FACTOR RELATIONS IN QUANTITATIVE INHERITANCE 189 
2. Typical Blending Inheritance-—Factors of allelomorphic characters 
blend in the heterozygote to form factors of intermediate character. 
The factors of the heterozygote are as uniform as those of either parent 
individual. 
3. Partial Blending Inheritance-—Factors of allelomorphic characters 
segregate in gametogenesis in the heterozygote, but with modification 
due to varying degrees of blending between the two allelomorphic factors. 
The first category here set off is that of ordinary Mendelian inherit- 
ance, and includes all cases in which there is admittedly no contamination 
by association of the members of an allelomorphie pair in the same 
individual. The second category calls for an assumption of factorial 
alteration to such an extent that all the factors of the parents as such 
disappear and only a factor determining an intermediate condition re- 
mains. The case may be illustrated abstractly in this fashion. Let the 
difference between two races genetically be that between A and a. 
The races are crossed. Now according to ordinary Mendelian assump- 
tions the factors A and a will segregate in the germ cells of the offspring 
and without factorial contamination. According to the assumption of 
typical blending inheritance, however, the two factors A and a when they 
meet in the hybrid immediately interact and this interaction gives an in- 
dividual having the genetic constitution A’A’ rather than Aa, the symbol 
A’ representing a factor intermediate in its character expression between 
Aanda. Asa consequence of this change in the factors involved such 
an individual, although of hybrid origin, is genetically not a hybrid and 
would consequently breed true. Admittedly the cases which fall into 
this category are not common, and it is a matter of debate whether any 
have thus far been found. As was pointed out in connection with the 
discussion of the conditions for a Mendelian interpretation of quantita- 
tive inheritance, the same relations find a consistent Mendelian explana- 
tion in those cases in which the number of factor differences is very large. 
The third category assumes that a variety of conditions may arise as 
the result of the production of an Aa individual. The blending may be de- 
finite so that A and a become A’ and a’, or it may be indefinite and give 
rise to a series of factors A;, Ao, As, . . . An and ai, de, a3, . . . Any 
all of which may be represented in the gametes of the heterozygous in- 
dividual. When definite factor contamination is assumed it may be 
regarded simply as an expression of the condition that the reacting 
system Aa reaches an equilibrium when it becomes A’a’, a condition for 
which there are many analogies in chemical reactions. In case some of 
the original factors still remain, such a heterozygous individual wouid 
produce gametes A, A’, a’, and a, which by conjugation would produce a 
variety of forms in its offspring. Insuch a case an individual AA’, or Aa’ 
might give rise to the establishment of a new equilibrium, but equally 
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