SEVENTEEN YEARS SELECTION OF A CHAR- 

 ACTER SHOWING SEX-LINKED MENDELIAN 

 INHERITANCE 1 



RAYMOND PEARL 



I 



In 1898 there was begun at the Maine Agricultural 

 Experiment Station an experiment in breeding Barred 

 Plymouth Rock fowls, having for its purpose the improve- 

 ment by selection of the character winter egg production. 

 This investigation has continued to the present time. A 

 resume of the results to date, considered with reference 

 to their bearing upon the general biological problem of 

 selection, may be of some interest. 



The experiment has fallen into three divisions or pe- 

 riods: viz., (1) the period from 1898 to 1907, (2) the 

 period from 1908 to 1912, and finally (3) the period from 

 1912 to date. Detailed reports on the methods of breed- 

 ing in operation have been published elsewhere. 2 For 

 purposes of clear orientation in the present discussion it 

 will be well here briefly to review the facts as to the 

 methods of breeding used in each of the periods. With 

 these facts definitely in mind wo may then proceed to an 

 examination of the results. 



1. The Period from 1898 to 1907.— During this period 

 the breeding followed the plan outlined at the beginning 

 by Woods and Gowell. Essentially it consisted of the 

 following elements. 



1. Trap-nest record of the performance of each indi- 



vidual female. 



2. Selection as breeders of all females which laid more 



than a definite number of eggs (150) in the first 

 laying year. 



i Papers from the Biological Laboratory of the Maine Agricultural Ex- 

 periment Station, No. 87. 



2 Cf. particularly Woods, C. D., and Gowell, G. M., U. S. Dept. Agr. 

 Bur. Anim. Ind. Bulletin 90, 1906, pp. 42; Pearl, B., and Surface, F. M., 

 Ibid. Bulletin 110, Part I, 1909, pp. SO; Ponrl, Mo. Agr. Expt. Stat. Ann. 

 Kept., 1911, pp. 113-176; and Pearl, Jour. Exp. Zool., Vol. 13, 1912, pp. 

 153-268 



595 



