Subject: Value of gene patents

Suppose someone deduces and patents a DNA sequence which is the gene for 
some property. Most (or all) genes merely specify amino acid sequences in 
a protein. But any amino acid can be specified by more than one base 
sequence. What legal barrier is there for someone to say,in effect, 
"Thanks for the sequence, I'll simply change a few bases which will not 
affect the final amino acid sequence and then I'll have my own gene which 
is not the one you patented"?  and then add, "Anyway, how do you know that 
the sequence you have patented is the only one extant for that gene. All 
you have patented is just one of maybe thousands of different sequences 
for that gene?"      

Re: Value of gene patents