A recent study of the eggs of tree frogs in Panama has provided insights into the concept of phenotypic plasticity. A biologist that studied the eggs observed that they would normally hatch a week after they were laid. However, by touching the eggs, the biologist could induce them to hatch immediately. The biologist likened this touch to the vibrations from an attacking snake. The implication was that the egg, even at an early stage, was flexible. It could either wait its usual full term to hatch, or hatch immediately in response to an environmental stressor. This example demonstrates phenotypic plasticity, which is the flexibility an organism has in expressing its genes. The phenotype is the expression of the genotype, or genetic makeup, and “plasticity” means the ability to change or adapt. Put another way, genotype is the inherited instructions that an organism receives from its genes, while phenotype is its physical appearance and actions.
Early theories of genetics relied on a cause-and-effect model: everything about an organism, including its phenotype, was determined by its genotype. Phenotypic plasticity, on the other hand, allows for the inclusion of environmental factors. For example, some types of plants can allocate more resources to their roots when growing in low-nutrient soil, or change the size and thickness of their leaves in response to the amount of sunlight they receive. Although genes certainly play a major role, individual organisms are not different simply because they have different genes. Rather, organisms can express phenotypic differences in response to variations in ecosystem, diet, temperature and climate.
The main purpose of the passage is to
A. (A) show how an experiment can replicate a naturally occurring situation
B. (B) define several scientific concepts and give examples of each
C. (C) introduce a theory and then discredit it
D. (D) demonstrate how one organism is similar to every other organism
E. (E) discuss a scientific theory and give some examples that support it