The AR gene contains two polymorphic trinucleotide microsatellites in exon 1. The substitution was localized in exon 3 and nonsense mutation at codon 68. The gene has been found to have missense mutation in exon 9. A polymorphism in the terminal exon of this mRNA results in two protein isoforms. In mRNA, codons also work as exon splicing enhancers. Quantification of sequence alignments may be performed at the gene, exon, or transcript level. This mechanism is an example of exon definition in splicing. These forms differ in alternative splicing of Exon 15 in their C-terminus. This suggests a haplotype dependency between exon 26 and other exon that have polymorphisms. Resistance mediated by an exon 20 C797S mutation accounts for the majority of resistance cases. I425V is a rare mutation on the ninth exon. The average exon encoded 30-36 amino acids. The flip/flop sequence is one such interchangeable exon. This results in a mature messenger RNA with a missing section of an exon.