164 



MENDELISM 



CHAP. 



•* ^- 



Lt^_»+ 



behaves as a simple 

 dominant to the normal 

 form, ie. that it depends 

 upon a factor which the 

 normal does not con- 

 tain. The recessive nor- 

 mals cannot transmit the 

 affected condition what- 

 ever their ancestry. 

 Once free they are always 

 free, and can marry other 

 normals with full confi- 

 dence that none of their 

 children will show the 

 deformity. 



The evidence avail- 

 able from pedigrees has 

 revealed the simplest 

 form of Mendelian in- 

 heritance in several 

 human defects and dis- 

 eases, among which may 

 be mentioned presenile 

 cataract of the eyes, an 

 abnormal form of skin 

 thickening in the palms 

 of the hands and soles of 

 the feet, known as tylosis, 

 and epidermolysis bul- 

 losa, a disease in which 

 the skin rises up into 

 numerous bursting 

 blisters. 



