INHERITANCE OF WINTER EGG PRODUCTION 85 



An alternative theory 



In working over this problem, another theory has been found, 

 whose ratios fit the observed ratios- equally as well as that 

 proposed by Pearl. In addition it has the following advantages: 



1. It is somewhat simpler since it does not involve sex linkage. 



2. It accounts genetically for the birds in the over-30 class 

 for which Pearl's theory requires a supplementary explanation. 



3. The only marked departures from the expected ratios are 

 downward, i.e., there is a deficiency of high producers. This 

 deficiency can be accounted for physiologically^ 



The alternative theory may be stated in this form. Winter 

 egg production falls into two classes, viz., high (over 30), 

 mediocre (under 30). The observed ratios agree with those 

 expected if it be assumed that high fecundity depends upon the 

 simultaneous presence of two factors, A and B, in the zygote, 

 while mediocre production depends upon the presence of not 

 more than one of these two factors in duplex, simplex, or nulli- 

 plex condition. The two factors are inherited according to the 

 usual dihybrid scheme. The theoretical ratios resulting are 

 shown in table 1.^ It will be noted that several classes of males 

 cannot be distinguished from each other by the progeny test 

 alone. Thus class 2 cannot be distinguished from 5, 4 from 8 

 and 6 from 7. The members of each pair can be distinguished 

 from each other only by the parental test. 



The ratios expected on Pearl's theory are given in table 2 

 (modified from Pearl, '12). 



The detailed reasons for grouping the zero class with the 

 mediocre producers have been discussed in another place (Good- 

 ale, '18) and need not be repeated here. It will be sufficient to 



. ^ The observed ratios cannot be explained by assuming a single factorial 

 difference between high and mediocre producers. Several more complicated 

 schemes, however, can be devised that furnish the desired theoretical ratios. 



^ The use of the form of the presence and absence theory does not necessarily 

 imply an acceptance of the view that material particles are present or absent. 

 Whenever a change takes place in a locus of a chromosome, it is clear that an 

 absence of the preceding condition occurs. Thus, A represents merely a con- 

 dition of a chromosome (or locus) different from a. 



