MENDELIAN CHARACTERS 201 



Hurst has already shown from an examination of the 

 stud book that the bay and brown colours of thorough- 

 bred horses are Mendelian dominants to chestnut. 



Other characters of the most diverse kinds are also 

 similarly inherited. We have already referred to 

 structural characters in maize and in peas. Stature 

 is a character which is definitely inherited in many 

 plants. Among more subtle characters a similar mode 

 of transmission has been found in the case of differences 

 in chemical composition, and in that of immunity 

 from and susceptibility to the attacks of certain 

 diseases. The thrum-eyed condition of the primrose 

 has been shown by Bateson and Gregory to be a 

 Mendelian dominant to the pin-eyed condition, so that 

 we have here the solution, so far as solution is possible, 

 of a biological problem to which Darwin devoted the 

 greater part of a volume. 



A study of numerous pedigrees has enabled Bateson to 

 show that there is great probability that in the case 

 of the human race certain congenital diseases are simply 

 transmitted from parent to offspring in accordance 

 with Mendel's law. 



How far the influence of the Mendelian principles 

 may extend we do not yet know. But it is certain that 

 very few, if any, cases have so far been discovered in 

 which differentiating characters do not behave in this 

 way when the types which exhibit them are crossed 

 together. Experiments have now been made upon a 

 great variety of plants and animals, involving a con- 

 siderable diversity of kinds of characters. Nevertheless 



