only subtle = characteristic of nuance?

Context:


Such disease studies -- the much-heralded "disease in a dish" approach -- and the search for potentially disease-modifying drugs require the use of cells and controls that are genetically identical, except for a specific alteration whose impact can then be observed.

"This is very relevant for diseases like Parkinson's, which likely will display only subtle phenotypes in the Petri dish. It is very important that the cells be genetically identical and have the same history, then make or remove only that mutation," says Whitehead Founding Member Rudolf Jaenisch. "If you use control cells from one person and a diseased cell from another person, it's like comparing apples and oranges."