Electrophoresis is used extensively in revealing genetic variation in enzymes and other proteins. In the case where all individuals in the samples reveal an enzyme with the same electrophoretic mobility it is called monomorphism. A hypothetical gel showing the stained bands can be seen below.


    __   __   __   __   __

all five bands display identical electrophoretic mobility (they are the same enzyme)

That shows how electrophoresis works in a more simple scenario in which the individuals are homozygous for an allele represented by the migrating enzyme, however, often you must take into account the presence of heterozygous individuals. Allozymes are enzymes that have differing eletrophoretic mobilites resulting from allelic differences at a single locus. For example, consider a hypothetical allele which exists in two forms; one associated with a rapidly migrating enzyme and the other associated with a more slowly migrating enzyme. When tested using gel electrophoresis, the results yielded will show three possible outcomes; homozygous for the rapidly migrating enzyme, homozygous for the slowly migrating enzyme and heterozygous for both rapid and slow enzymes. This means that in homozygous individuals only one band will appear in the gel, representing either rapid or slow enzymes, and in heterozygous individuals two bands will appear, once stained, to represent both rapid and slow enzymes.

Monomeric Polymorphism
     __    __         __               
     __          __   __     __         
                                         R= rapid   
     R/S   R/R  S/S   R/S    S/S         S= slow

In the above example the enzyme itself is monomeric, meaning it consists of only one polypeptide chain, so the heterozygous individual will show the two possibilities of a rapid enzyme and slow enzyme; each enzyme representing a single allele. However, if the enzyme were a dimer, molecularly consisting of two polypeptide chains, three possibilities arise; enzymes containing two rapidly migrating polypeptides, two slowly migrating polypeptides, and both rapidly and slowly migrating polypeptides. The rapidly migrating (rapid + rapid) and slowly migrating (slow + slow) homodimers behave in a similar manner as in the case of a monodimer, but the heterodimer (rapid + slow) will typically have an intermediate electrophoretic mobility. In the case of multimeric (consisting of multiple polypeptide chains) enzymes the outcome becomes increasingly complex.

Dimeric Polymorphism
  __                  __              
  __        __                          RR= rapidly migrating homodimer   
            __                  __      SS= slowly migrating homodimer
                                        RS= heterodimer (rapidly + slowly migrating)
RR/RS      RS/SS     RR/RR    SS/SS