Which of the following is an example of a known recurring and predictable source of variation?

• A. Age
• B. Unexpected disease outbreak
• C. Random measurement error
• D. Genetic mutation

Answer: (A)

Age stands out as a known recurring and predictable source of variation because biological traits change in a systematic way as an organism develops. In breeding and genetics studies, measurements taken at different ages reflect predictable stages of growth and maturation, so age can be planned for or modeled as a fixed effect. This makes age a reliable driver of variation across a population, unlike the other options. An unexpected disease outbreak can alter results unpredictably, random measurement error introduces noise that isn’t consistently repeatable, and a genetic mutation is rare and not a regular, forecastable source of variation in a population.