Molecular Genetics

Enzyme polymorphisms (allozymes) can be used as molecular markers on the genetic chromosome.

Facts

• Enzymes are macromolecular catalysts. Most enzymes are proteins. Each enzyme catalyzes a specific chemical reaction. For some enzyme reactions, methods exist that produce a color change at the site of reaction, allowing location of the enzyme.
• An example of an electrophoretic analysis of one hypothetical enzyme is shown. Extracts of cells of different individuals (numerals) were subjected to gel-electrophoresis. The gel was then stained to reveal the position of the enzyme activities. Individuals 5 and 6 were the parents of 7. An actual photograph of a result (from Univ. Conn.) is at right
• Note that some individuals have a single band, others have three, but none have two.

Interpretations

• The active enzyme is a homodimer. When both fast (F) and slow (S) alleles are present, three kinds of homodimer are formed: FF, FS, and SS.
• The alleles are codominant. Bands additional to those of the homozygous parents are seen for multisubunit enzymes in heterozygotes.
• Enzyme polymorphisms (allozymes) can be used as molecular markers on the genetic chromosome.

Further information

• Isozyme refers to polymorphic enzymes that result from different loci, while the term allozyme is reserved for allelic enzymes.
• Allozyme polymorphisms are also used in phylogenetic and population analysis.
• Allozymes are fairly easy to evaluate by laboratory experiments and are a resource in plant genetics.
• Enzyme alleles can sometimes also be detected by their products, such as the blood group antigens.