forms of a protein produced from different genes, or from the same gene by alternative splicing

A protein isoform is any of several different forms of the same protein. Different forms of a protein may be produced from related genes, or may be made from the same gene by alternative splicing. A large number of isoforms are caused by single-nucleotide polymorphisms or SNPs, small genetic differences between alleles of the same gene. These occur at specific individual nucleotide (building block of dna-strand) positions within a gene.