40 Genes and Characters 



duces a curious condition that apparently is not harmful in 

 the least. Individuals with this dominant gene have a depres- 

 sion in the chest that looks as if it had been produced by a ball 

 that had been pressed in. A far more harmful gene is the 

 dominant that produces cartilaginous growths on the bones. 

 Another dominant gene affects the bones in such a way that 

 they are easily broken; a person with this gene may have a 

 couple of dozen bone fractures during the course of his life. 



Several types of dwarfism, or nanism, are inherited. The ateli- 

 otic type or midget, in which the individual is correctly propor- 

 tioned but much smaller in every way than a normal person, 

 results apparently from the interaction of two dominant genes. 

 The achondroplastic type appears also to be the result of two 

 interacting dominant genes. When both dominants are present, 

 the person has shortened limbs but a normal-sized trunk. Both 

 types of dwarfs may be found in side-shows. 



Abnormalities of the fingers and toes are fairly numerous. In 

 Polydactyly, a condition that has been reported a number of 

 times, the individual has extra fingers or toes. A number of 

 families of the white race have been studied in which this 

 character appears to result from a dominant gene. Negroes 

 with Polydactyly apparently are homozygous for a different 

 gene which is a recessive. Hefner has recorded an interesting 

 case of a dominant gene for Polydactyly which is very variable 

 in its expressivity. In some individuals, the terminal joint of 

 the thumb is long and slender and tends to taper to a point, but 

 the thumb is otherwise normal. Other individuals have thumbs 

 which are long and finger-like and usually bent at a very decided 

 angle toward the index finger. In still others, there may be an 

 extra thumb which is joined to the metacarpal of one or both of 

 these finger-like thumbs while an extra toe is present between 

 the big toe and the normal second toe. This condition appears 

 to be the result of one dominant gene, but it has appeared rather 

 irregularly in several families, indicating probably a gene with 

 reduced penetrance. Other characters affecting the digits are 

 syndactyly, or webbed fingers and toes, which appears to be due 

 to a dominant gene in some families and a recessive in others, 

 brachydactyly, in which a dominant gene results in the absence 

 of the middle phalanx of each finger, causing it to be considerably 



