The best explanation for the observation that a single change in the gene encoding α-keratin results in multiple effects (frizzled feathers, increased food consumption, higher heart rate, and delayed sexual maturity) is Pleiotropy.
Pleiotropy occurs when a single gene influences multiple phenotypic traits. In this case, the mutation in the α-keratin gene affects various physiological and morphological traits in the chickens, demonstrating the concept of pleiotropy.