What defines an individual's phenotype?

An individual's phenotype is defined as the sum of observable traits. This includes physical characteristics such as height, eye color, hair type, and other traits that can be seen or measured. The phenotype results from the interaction between an organism's genotype (the genetic makeup) and the environment.

This means that even if two individuals share the same genotype, their phenotypes may differ due to environmental factors, development, or other influences. Understanding phenotype is crucial in fields such as genetics, biology, and medicine, as it helps explain how traits are expressed in living organisms and can be impacted by various external factors.

The other options, although related to biology, do not accurately define phenotype. Species classification pertains to taxonomy, the number of chromosomes relates to genetics but does not encompass the traits that are observable, and the genetic sequence of DNA refers specifically to the organism's genotype rather than the outward expression of that genotype in the form of traits.