Discontinuous variation features distinct categories without intermediates

Steps:

• Recall discontinuous variation involves traits in clear groups, like discrete phenotypes, unlike continuous traits that vary gradually.
• Examine choices: Identify which human trait shows no blending or intermediates.
• Compare to examples: Blood groups are categorical (A, B, AB, O), while others measure on a spectrum.
• Confirm: Genetics supports blood groups as discontinuous due to alleles producing fixed types.

Why B is correct:

• Blood groups exhibit discontinuous variation as they fall into distinct, non-overlapping categories (A, B, AB, O) determined by specific alleles, with no intermediates.

Why the others are wrong:

• A: Body weight is continuous, varying gradually due to multiple genes and environment.
• C: Height is continuous, showing a range of values influenced by polygenic inheritance.
• D: Skin colour is continuous, blending across a spectrum from light to dark via multiple genes.

Final answer: B