Final answer:
Personality is the trait least likely to be purely determined by heredity, as it is influenced significantly by environmental factors and experiences, unlike traits such as eye color and blood type which have a stronger genetic basis.
Step-by-step explanation:
Of the traits listed - eye color, height, personality, and blood type - personality is the least likely to be affected purely by heredity. While traits like eye color, height, and blood type have a strong genetic basis, personality is a complex trait influenced by an interplay of genetic predispositions and environmental factors.
Eye color is not controlled by a single gene but rather by multiple genes involved in the production and distribution of melanin. Someone who is albino, for instance, cannot have brown eyes because the disorder is characterized by a lack of melanin, which is necessary for developing brown pigmentation in the eyes. Furthermore, polygenic inheritance, as seen with traits like height and skin color, involves multiple genes contributing to a characteristic, which violates Mendel's rules that imply traits are controlled by a single gene with dominant and recessive alleles.
While genetic inheritance plays a substantial role in influencing traits like eye color and height, it is environmental factors such as nutrition and exposure to sunlight that can modify their expression. Personality traits, although having some genetic component, are largely shaped by one's environment and experiences, illustrating the intricate relationship between genes and the environment.