Which description best describes an amorph?

• A. A gene that is always recessive
• B. Gene with no directly observable product
• C. A gene located on the X chromosome
• D. A gene that has multiple phenotypic effects

Answer: (B)

An amorph is a gene that has no detectable product. In immunohematology this means the antigen normally produced by that gene isn’t expressed on the red cell surface, so serologic testing cannot detect that antigen. The defining feature is the absence of a directly observable product, not inheritance pattern, chromosomal location, or pleiotropy.