INDEPENDENT MENDELIAN INHERITANCE 95 
For the experiment a wild male of the genetic formula AA BBDDPP 
was mated to a pink-eyed dilute brown female of the genetic constitution 
aabbddpp. The Fis, AaBbDdPp, displayed all four dominant characters 
and were like the wild males. The F. segregation is shown in Table XIV. 
For 1180 individuals only about four times the number of genetic com- 
binations for a four-factor hybrid, the agreement is satisfactory. 
As for the chromosome interpretation, it may be made in the same 
way as in other cases by assuming that four different pairs of chromo- 
somes bear the factors. Sixteen different kinds of gametes would be 
formed by such a hybrid, and these together would give the 256 gametic 
combinations of the F'2. generation. 
For higher numbers of pairs of factors the same manner of independ- 
ent distribution may hold as for those cases which have been outlined in 
detail. For independent distribution, the chromosome condition is 
simply that the different pairs of factors be borne in different pairs of 
chromosomes. Since, however, the total number of factors in any species 
must greatly exceed the number of pairs of chromosomes, it cannot be ex- 
pected that every multi-factor hybrid will display independent segregation 
for all its factors. The number of pairs of chromosomes in Drosophila is 
four, consequently no crosses in this species involving more than four pairs 
of factors can possibly display independent segregation, if the chromosome 
theory be valid. Moreover, on the basis of the laws of probability, the 
chances that any particular case of even fourfold factor hybridization 
in this species would display independent segregation are extremely 
slight. Abundant evidence in this species has established the validity 
of these theoretical deductions. The same principles may logically 
be extended to other species so that for even as small a number of pairs 
of factors as five in wheat, which has eight pairs of chromosomes, in peas 
which have seven, and in corn which has ten, independent segregation 
would be an exception rather than the rule. Cases where independent 
segregation does not occur are treated in the next chapter, which deals 
with linkage. 
Methods of Dealing with Genetic Data——Many different methods 
have been devised for representing the results of Mendelian studies, and as 
yet the work of any large group of investigators is marked by a consider- 
‘able lack of uniformity in this respect. Often the same investigator 
employs at one time one method of representation, and at another time, 
another. This is as it should be, for it can hardly be expected in a field 
of investigations marked by as rapid strides as had been characteristic of 
genetics in recent years that the ideal method of presentation should have 
been discovered while only a comparatively small portion of the evidence 
is at hand. Moreover, the method of presentation is merely a short- 
hand account of the operation of certain principles; it should not, there- 
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