Final answer:
To determine the influence on a phenotype, genetic factors, environmental conditions, and G x E interactions are assessed by observing trait expression under various environmental conditions and comparing them with genotypic variations.
Step-by-step explanation:
To differentiate whether a phenotype is affected by genetic, environmental, or Gene x Environment (G x E) interaction, we must observe how traits are expressed under different conditions. Genetic variation in phenotypes is due to different alleles inherited from the parents, as demonstrated in Mendel's experiments with pea plants, where crossing plants with green and yellow pods resulted in offspring with a mix of these colors across generations. The observable traits, or the phenotype, were influenced by the genotype, consisting of both exposed and non-expressed alleles. Environmental effects, such as sun exposure affecting skin color, show that the same genes can lead to different phenotypes under varying environmental conditions. With G x E interactions, both genetic makeup and environmental factors play a role, such as temperature-dependent sex determination in reptiles, where the same genotype can produce either male or female offspring depending on the incubation temperature of eggs.
It is essential to recognize that while genetic variation can be passed down to offspring and subject to natural selection, environmental effects on phenotypes cannot be inherited. Therefore, to decipher the influence of genetics versus environment, scientists observe the trait variations among individuals with the same genotype under different environmental conditions. Over 100 years of genetics studies have improved our understanding of phenotype expression, but complex traits and diseases, often involving multiple genes and environmental factors, still present challenges in separating the genetic and environmental contributions.