Re: Why is the trait for polydactyly dominant??

Polydactyly (an abnormal numbers of digits) can be associated with over 
150 different conditions, and , occasionally, can be inherited in some 
familial conditions as a dominantly inherited trait.  However, this is 
usually caused by a mutation in a gene involved in proper limb 
development.  Frequently, polydactyly is part of a more complicated 
picture (or syndrome) in which other abnormalities are present.  Sometimes 
these are fatal or life-threatening, so the mutation is not passed on to 
future generations.  In families with isolated inherited polydactyly (no 
other abnormalities) 50% of an affected indvidual's children will also 
have this trait, so in this family the number of children with 5 digits 
would be equal to those with more that 5.  However, these mutations and 
these families are rare, so the vast majority of us have 5 digits.