Non-synonymous DNA SNPs may result in the substitution of one amino acid by another with a different electrical charge (interchanges of -, 0, or + charges) that result in slight modification of the net charge of the protein. These protein variants are called allozymes because they are encoded by different alleles at an enzyme gene locus. A protein electrophoresis experiment will show charge differences in allozymes as faster or slower mobility in an electric field: these might be described as "slow", "medium", or "fast", and annotated as (for example) ADHs, ADHm, and ADHf. Allozymes should not be confused with isozymes, which are different forms of the same enzyme encoded at different gene loci. Isozymes might be designated ADH-1 and ADH-2, with different sets of allozymes.
The bands seen on an electrophoretic gel are thus protein
products that indicate the presence of SNP variants
in the corresponding protein-coding exon regions. As
geneticists, it is important to distinguish between the electrophoretic
evidence for SNP variation and the SNP itself:
bands on gels are not "alleles".
It is also important to remember that (1) many SNPs are
synonymous and do not result in an amino acid
substitution, (2) some non-synonymous SNPs may not
result in amino acid substitutions with charge changes,
and (3) some charge changes may not affect the mobility of the
allozyme product, for example if the change occurs in the
inner part of the protein.