BROODINESS IN DOMESTIC FOWL. 



107 



i.e., the number of times a bird becomes broody as well as the ease with 

 which she is broken up, vary considerably, as already described. Since 

 the chief reason for this variability is found in the number of times a bird 

 becomes broody, which in turn is so thoroughly interwoven with egg 

 production, the same practical difficulties, i.e., disease control, that at 

 present prevent a complete analysis of the inheritance of fecundity also 

 prevent the determination of the hereditary factors involved in degree 

 of broodiness. 



The Production op a Strain op Low Degree op Broodiness through 

 Selection. 



Two lines of selection have been under way, — one for the elimination 

 of broodiness, the other for its development to a high degree, equal to or 

 greater than that observed in the case of Fig. 1. Because most of our 

 facilities were needed in other directions, little has been done with the 

 plus line beyond its maintenance. The minus line, however, has been 

 closely involved with the problem of securing increased egg production, 

 since absence of broodiness tends toward higher production, other things 

 being equal. Until 1917 this hne had been also carried on in a very small 

 way, the general policy being to mate the son of a non-broody bird to 

 non-broodies, on the hypothesis that broodiness is a simple Mendelian 

 dominant, and non-broodiness a recessive. As a result of the early matings 

 a male was obtained that appeared to be a homozygous recessive, since 

 he threw no broodies from non-broody mothers. In 1917 this male, No. 

 3003, with his son. No. 5470 out of a non-broody hen, and grandson. No. 

 9752 (mother broody once in her third year), also supposed to be homozy- 

 gous recessives, were mated to all the non-broody hens available. Some 

 of these, however, became broody the second year. The results of the 

 experiment, given in Tables IV and V, show that non-broodiness is not 

 always a simple MendeUan recessive, since the son and grandson failed 

 to breed true, even with those birds that never became broody. This 



Table IV. — The Progeny of Three Supposedly Non-broody Males dis- 

 tributed according to their Mother's Broody History. 



