No. 606] SHORTER ARTICLES AND DISCUSSION 373 



gene G should be stably related to its new position in cliromo- 

 some C it must be held incorporated by force F^, and not by 

 force Fg as is the case. Added on to the original problem of the 

 interchange of the genes is now the second and equally imposing 

 problem of the interchange of the forces subsequent to the inter- 

 change of the genes. An actual bodily interchange of the forces 

 seems impossible in view of the assumptions we have had to make 

 as to their nature and action. The transformations would then 

 have to be accomplished by some transnuitation in situ. It is 

 evident that no interiuil autonomous cliange short of a complete 

 and absolute mutation of force F^' in chromosome C into Fg and 

 simultaneously of Fg in C into F« would suffice. But we liave 

 no precedents for assuming such reciprocal mutations, and if we 

 had, we could have sidetracked this whole machinery by applying 

 this reciprocal transmutation idea to tht> genes and thereby 

 solved the first problem in such a way that the second cduld not 

 arise. Instead of localizing the cause of The iv,-!,., n,.,il n.nisfor- 

 mations of the forces in the forces themselv.-. ni,r miuiit iiMiisfor 

 it to the genes; i. r., one nuuht endow tl)e genes with the power 

 of causing reciprocal t i-iiiist'oniiiitioiis of the forces rather than 

 empower the forces to t r;iiisiiuiiiiie of their own accord. While 



of plausibility, it ean iioi he t;ikeii ;is more than an attempt at 

 formal escape from t lie (lifliciiliy a lift nm- of one's self by one's 



prop(n-ty (if -eiies which needs, as siipi)ort. only such formal ex- 



Calvin B. Bridges 



ON THE PROBABLE ERROR OF MEXDELIAX CLASS 

 FREQUENCIES 



An old friend of geneticists who dislike excessive calculation 

 has recently been attacked by Pearl, ^ viz., the familiar formula, 

 a==\/npq for the standard deviation of a Mendelian class fre- 

 quency. He proposes to substitute a more refined but much more 

 complicated method, originated by Pearson. In a Mendelian 

 illustration he obtains a result which differs by over 40 per cent. 



1 Pearl, B., "The Probable Error of a Mendelian Class Frequency," 

 American Naturalist, Vol. LI, pp. 144-156, 1917. 



