Final answer:
The main difference between phenotypic variance and heritability is that phenotypic variance encompasses all variances in traits including environmental causes, while heritability only accounts for variance attributable to genetic differences.
Step-by-step explanation:
The difference between phenotypic variance and heritability revolves around the concept of how traits are expressed and passed down in organisms. Phenotypic variance refers to the observable variation in physical traits among individuals of a population, which can be influenced by both genetic factors (genotype) and environmental conditions. On the other hand, heritability is a measure that represents the proportion of this variation that is due to genetic differences among individuals. High heritability means that genetic factors play a larger role in the phenotypic variation of a trait within a population, thereby indicating the potential for evolutionary change in response to natural selection.
Heritability does not tell us how much of an individual's phenotype is determined by its genetics, but rather, how much of the variability in a trait within a population can be attributed to genetic differences. For instance, consider Mendel's experiments with pea plants. The genotype determines the potential for certain phenotypes, such as seed color, while the environment can also influence the expression of these genes. When evaluating a trait's heritability, it's important to understand that it applies to the population level, not to the individual level.