Which of the following is an example of an environmental factor that can influence phenotype?

The correct answer highlights the role of environmental factors, such as temperature and nutrition, in influencing the phenotype of an organism. Phenotype refers to the observable characteristics or traits of an organism, which can be affected not only by its genetic makeup but also by various environmental conditions.

For instance, in some species, the temperature during development can affect physical traits, such as coloration in reptiles, which may vary based on the temperature of their environment. Additionally, nutrition plays a crucial role in determining growth, size, and overall health, which are important aspects of phenotype. Adequate or inadequate nutrition can lead to differences in body composition and development, showcasing how environmental conditions shape the external traits of an organism.

In contrast, traits like eye color and blood type are primarily determined by an individual's genetics and are not influenced by the environment. Genetic mutations can alter the genotype and potentially lead to changes in phenotype, but they are not classified as environmental factors. Thus, the example given illustrates the significant impact of external conditions on phenotypic expression.