Final answer:
The relation between genotype and phenotype is complex for quantitative characteristics due to the involvement of multiple genes, various gene interactions, and environmental influences. Skin color and adult height are examples of polygenic characteristics with a wide range of phenotypes.
Step-by-step explanation:
The relation between genotype and phenotype is frequently complex for quantitative characteristics because these characteristics are usually controlled by multiple genes rather than a single gene. These genes can interact with each other in various ways, such as codominance and incomplete dominance. Additionally, environmental factors can also influence the expression of these genes, further complicating the relationship between genotype and phenotype.
For example, human skin color is a polygenic trait that involves the action of multiple genes. Each gene contributes to a certain extent to the overall skin color, resulting in a wide range of phenotypes. The same complexity applies to other quantitative characteristics, such as adult height. These characteristics exhibit a continuous variation instead of discrete categories, making it more difficult to determine the exact genotype-phenotype relationship.