216 MULTIPLE ALLELOMORPHS 
or part of the body that is affected. It seems there- 
fore more probable that this peculiar fact. connected 
with multiple allelomorphs means that the same 
portion of the chromosome is changed in one or 
another direction. 
3. Itis true that a very wide range of linkage values 
has been obtained, that extends from almost free 
segregation to less than 1 per cent. of crossovers. 
However, if we should construct a curve showing the 
number of cases exhibiting the various possible 
linkage values, the number showing complete linkage 
or, as we should say, multiple allelomorphism, would 
be far in excess of the number of these to be expected 
from the general shape of the rest of the curve. This 
indicates that multiple allelomorphs are in a class 
by themselves, not merely extreme cases of the same 
type as an ordinary linkage case. 
4. There is an a priori consideration that may not 
be out of place in the argument. There is no suffi- 
cient reason for supposing that only one sort of 
mutation can occur in a given locus in the chromo- 
some. If the basis of the chromosome is a chain of 
chemically complex substances (e.g., proteins), any 
slight addition or loss or even re-arrangement of the 
atoms in the molecules of a bead in such a chain 
might well produce an effect on the organism, and 
perhaps a more marked effect on that particular 
character that stands in closest relation to that 
chemical body. Since we know that mutations and 
even “reverse”? mutations actually occur, it would be 
indeed strange if only one kind of change were 
