@Michael J.Benedic thanks for your response my specific question is " from the enzyme guide I prepare the enzyme with buffer, ddH2O, and product of PCR (specific gene) as in guide paper .. after oncubation time for 100 samples (normal and patients) I did electrophoresis but without cutting to determine allel ... all bands were the original of gene and M. weight !!! ?
The first thing is to be sure your HinfI enzyme is working properly. Perhaps you can do a test digest on some pure plasmid DNA.
Secondly, I presume you know for certain that HinfI cuts your PCR product, in other words that the region of the gene you are amplifying actually has the HinfI restriction site?
Lastly, perhaps you can upload a picture of the gel, that might help diagnose if something else is the matter.
Regarding the first point, you should be able to test the enzyme just on some plasmid DNA from the lab.
Secondly, you should be able to determine the DNA sequence of the region you amplify from Genbank, and then just analyze it for HinfI restriction sites.