Some Mendelian Considerations arising 

 from the Pedigree on Lenticular Cataract 



BY THE EDITOR. 



Two features seem clear in the Pedigree of Lenticular 

 Cataract described by Dr. Rutherfurd. First, it is not a 

 case of simple Mendelian inheritance. Second, the 

 segregation of affected and non-affected members is 

 quite clean. Dr. Rutherfurd made an examination of 

 the eyes of some of the unaffected persons and though 

 they were of the age, or in some cases older, than other 

 members of the same generation in which the defect 

 had appeared, they themselves manifested no sign of 

 cataract. In as far therefore as we have this clean 

 segregation of affected and non-affected individuals the 

 pedigree exemplifies a Mendelian mode of inheritance. 



We may next consider the complexities it presents 

 from the Mendelian standpoint. In the first place, the 

 affected persons produce an offspring containing both 

 affected and non-affected. This is the case whether 

 both parents are affected, as Nos. 14 and 21 in generation 

 B, or whether one parent onlj- presents the defect as 

 with No. 19 and his wife in the C generation. Now, 

 this being the case, on a simple Mendelian basis we should 

 regard the normal condition as being recessive and the 

 defective as a dominant character. But then the normal 

 parents cannot, in a simple Mendelian case, produce 

 affected offspring. The fact that this has occurred 

 in a son of No. 2, A generation, and in a daughter of 

 Nos. 3 and 4 of the same generation, all of them being 

 normal parents, clearl}^ shows this case to be complicated 

 by the presence of two or more congenital factors. 



Something of a very similar nature is shown in several 

 of Mr. Nettleship's pedigrees of cases of retinitis pig- 

 mentosa. There normal parents produce some affected 

 offspring, and affected parents also produce a mixed 

 offspring of affected and unaffected members. Many 



