The term ‘polygenic inheritance’ refers to:

The correct option is Multiple genes controlling one trait.

Step 1: Understand the terminology
The word polygenic is derived from two roots: "poly-" meaning many, and "-genic" referring to genes. Therefore, polygenic inheritance literally means inheritance influenced by multiple genes.

Step 2: Define Polygenic Inheritance
Polygenic inheritance occurs when a single phenotypic trait is controlled, influenced, or determined by the quantitative and additive effects of two or more independent genes. Examples in humans include height, skin color, eye color, and intelligence.

Step 3: Evaluate the given options

1. One gene controlling multiple traits: This phenomenon is called pleiotropy (not polygenic inheritance).
2. Multiple genes controlling one trait: This is the correct definition of polygenic inheritance.
3. Mutation in a single gene: This refers to a point mutation or monogenic alteration.
4. Duplication of chromosomes: This refers to polyploidy or chromosomal duplication, which is a structural/numerical chromosomal alteration.

Thus, polygenic inheritance specifically refers to multiple genes controlling one trait.