LECTURE VI 

 HEREDITY IN MAN 



MOST of our knowledge of inheritance in man has had 

 perforce to be acquired by methods different to those 

 used with the lower animals, or plants, owing partly to 

 the fact that the experimental method is inapplicable, 

 and partly to the fact that the characteristics in which 

 we are for practical reasons most interested in man, are 

 apparently not simple ones in the Mendelian sense i.e. 

 depending for their expression on only one or few factors 

 in the germ-plasm, but complex ones depending upon 

 the interaction of many. 



Some simple cases of Mendelian inheritance in man are 

 known, however, most of them concerning abnormalities. 

 The inheritance of the condition known as Brachydactyly, 

 or short fingers, is shown in the family history summarised 

 in Fig. 49, the pedigree reading from above downwards 

 as in the case of Fig. 48. Persons with this abnormality 

 possess only two joints to the fingers and toes instead of 

 three. All fingers and toes are affected alike, and the 

 condition is associated with shortness of stature. 



The first point to notice is that no case is known of 

 two brachydactylous persons marrying each other. Hence 

 the wives or husbands of the persons appearing in the 

 pedigree are not shown, they being all normal. 



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