Continuous variation from polygenic and environmental influences

Steps:

• Observe the data: foot lengths form a range (20-26.9 cm) with varying frequencies, showing a bell-like distribution despite gaps.
• Identify variation type: measurements in decimals indicate continuous trait, not discrete categories.
• Recall causes: continuous traits like height or foot length result from multiple genes (polygenic) plus environmental factors like nutrition.
• Match to options: polygenic inheritance plus environment fits continuous variation.

Why A is correct:

• Continuous variation is defined as polygenic (multiple genes) combined with environmental effects, producing a smooth range of phenotypes as in foot length data.

Why the others are wrong:

• B: Ignores genetic role; environment alone cannot explain heritable continuous traits.
• C: Discontinuous variation involves single genes with distinct categories, not a ranged distribution.
• D: Discontinuous applies to discrete traits like blood groups, not this measurable continuum.

Final answer: A