lOO INHERITANCE IN POULTRY. 



E. SUMMARY OF CONCLUSIONS. 



(i ) Poiiltr3' exhibit numerous unit characteristics which do not blend in 

 hybridization, but are inherited in ahernative fashion. The unit characters 

 are not immutable things in hybrids, but subject to modification — perhaps 

 permanent — by interaction of the alternative characters. 



(2) Although the great majority of characteristics of poultry are inherited 

 alternativelj', yet a few cases of color characters show a particulate inher- 

 itance. The comparative rarity of blending of characters makes it easier to 

 see how new characters will not be "swamped by intercrossing with the 

 parent form " (page 82). 



(3) Specific and varietal characteristics in de Vries's sense are not inherited 

 in a markedly different fashion, although in two cases progressive variants 

 do not Mendelize typically. 



(4) The patent characteristic is usually dominant over its latent allelo- 

 morph. 



(5) Old and new characteristics are equally dominant. 



(6) Dominance and recessiveuess of characteristics are not always accom- 

 paniments of their segregation in the germ cells; both, moreover, are fre- 

 quently incomplete. 



(7) Dominance is usually, but not always, independent of the races crossed. 



(8) Prepotency is as truly important in inheritance as dominance. 



(9) Many first hybrids exhibit special forms, due to the interaction of the 

 two allelomorphs. These may become fixed as new characteristics. 



(10) Reversion is being explained by the persistence in a "latent" 

 condition of the latent cliaracter. 



(ix) An adequate theory of gametic purity has not only to explain the 

 simple Mendelian formula, but also the facts of imperfect dominance, im- 

 purity of extracted forms, latency and atavism, and occasional particulate 

 inheritance. 



("12) Reciprocal crosses exhibit differences due to the fact that the father 

 and the mother transmit different kinds of characteristics. 



( 1 3) When the parent races are dimorphic each sex in the hj^brids exhibits 

 the respective sex characteristic of both of the species. In many cases a 

 new form of sexual dimorphism appears in the hybrids. 



(14) Certain characteristics of one sex may become transferred to the 

 other by hybridization, owing to lack of complete correlation between primary 

 and secondary sex characters. 



(15) The proportion of the two sexes in hybrids is normal. 



(16) With few exceptions, correlated characteristics easily separate as a 

 result of hybridization so that anj' conceivable combination may be effected. 



Carnegie Institution, 



Station for Experimental Evolution, 



Cold Spring Harbor, February 12, igo6. 



