INDEPENDENT MEN DELI AN INHERITANCE 95 



For the experiment a wild male of the genetic formula AABBDDPP 

 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 2 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 z 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- 



