LXIV 



BOWMAN LECTURE. 



called a dominant over the normal condition, in other cases 

 as a recessive. Bat since the victims of the same hereditary 

 disease, be it purely dominant or purely recessive, scarcely 

 ever intermarry, no trace of pure disease is established. 



In most cases, using Mendelian terms, an hereditary 

 disease is transmitted by the mating of an impure, or 

 hybrid, dominant (D.R.) with a recessive (R.R., Fig. 6 E), 



Inheritance 



Theoretical 

 oi Frrat 



I DD x DU 



B 

 BOX RR 



tt JttD-DU 



Rare i" Human Disease 



DR-DR 



f\]\ the 



v/ohtn Dfsea5f Recessive 

 c Normal 



K DJ)-DR-DR-RR 



Common uJhen Biseas? ' 



DR-RR 



Commonest -forrrt : Dise<xe 

 eitViev Domin&.nft ov Recess twC 

 '/I oi Of4s)vmc| Dist<xsed fn 

 case.. 



and if sufficiently large numbers be taken half of the result- 

 ing offspring should be normal and half diseased, whether 

 the disease be the dominant or the recessive partner. 



If the disease be dominant it is of course rare for 

 mating to occur between two persons suffering from it. 

 When such union does occur all the offspring should be 

 diseased if the dominance in one parent or both be pure 

 (Fig. 6 A, B, and c), three quarters if both parents be 

 hybrid dominants (Fig. 6 D). 



