Factors Influencing Continuous vs. Discontinuous Variation

Steps:

• Define continuous variation as traits showing a range of phenotypes, like height or skin color.
• Define discontinuous variation as traits with distinct categories, like blood groups or pea pod color.
• Identify causes: continuous variation results from both genetic and environmental factors; discontinuous variation results primarily from genes.
• Match to option D, which correctly assigns "both environment and genes" to continuous and "genes only" to discontinuous.

Why D is correct:

• In biology, continuous variation follows a polygenic inheritance model influenced by multiple genes and environment (e.g., quantitative traits), while discontinuous variation is monogenic and minimally affected by environment (e.g., Mendelian traits).

Why the others are wrong:

• A: Incorrectly attributes both factors to discontinuous variation, ignoring its genetic dominance.
• B: Wrongly limits continuous variation to environment only, overlooking genetic contributions.
• C: Falsely assigns genes only to continuous variation, neglecting environmental effects.

Final answer: D