BLENDING INHERITANCE 181 



in potency, which are either of the formula DD or DR, 

 may, if bred inter se, give a various progeny among 

 which the dominant character D is likely to again 

 become manifest, while recessives, of the formula 

 RR, on the contrary, will always give offspring which 

 all agree in the entire absence of the character in 

 question. 



Davenport cites an extreme case of failure of potency 

 in one of two rumpless cocks from the same blood. 

 The character of rumplessness is due to an inhibitor 

 of tail development. That these two cocks both 

 possessed this character was demonstrated by the 

 entire absence of any tail in either case. The in- 

 hibiting determiner for tail growth was so weak in 

 cock No. 117, however, that, to quote Davenport's 

 exact words : "In the heterozygote the development of 

 the tail is not interfered with at all, and even in ex- 

 tracted dominants it interfered little with tail develop- 

 ment, so that it makes itself felt only in the reduced 

 size of the uropygium and in-bent or shortened back. 

 But in No. 116 the inhibiting determiner is strong. 

 It develops fully in about 47 per cent of all the 

 heterozygotes and in extracted dominants may pro- 

 duce a family in all of which the tail's development 

 is inhibited." 



Here were two birds of the same blood, pheno- 

 typically alike and presumably genotypically . alike, 

 which because of an individual difference in the 

 potency of the determiner for rumplessness produced 

 quite different results in their offspring although bred 

 to precisely the same array of hens. 



