Which of the following best defines phenotype?

Phenotype refers to the observable physical properties of an organism, which include traits such as appearance, development, and behavior that result from the interaction of its genotype (the organism's genetic makeup) with the environment. Selecting the option that defines phenotype as the physical expression or characteristics of a genotype accurately captures this concept.

In genetics, while the genotype provides the underlying information encoded in the DNA, the phenotype is what is manifested in the organism. This includes traits like height, eye color, and the ability to metabolize certain substances, all shaped by gene expression influenced by environmental factors. Understanding this relationship highlights why phenotype is essential in the study of biology as it connects genetics with observable features.

The other options focus on different concepts; for instance, one option describes genotype, another relates to evolutionary concepts, and a third discusses variation among individuals rather than defining what phenotype specifically entails. By understanding that phenotype encompasses the physical manifestations derived from genotype, the definition becomes clear and applicable in biological sciences.