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Difficulty: MediumHuman Morphological and Physiological Variations

During a practical biology lesson, students recorded various inherited characteristics among their classmates, including height, blood group, fingerprint patterns, and phenylthiocarbamide (PTC) tasting ability. Which of these traits is correctly classified as a physiological variation that exhibits discontinuous variation?

  1. Ability to taste phenylthiocarbamide (PTC)Answer
  2. B
    Fingerprint ridge patterns
  3. C
    Human skin pigmentation
  4. D
    Body weight in adult humans

Answer

Ability to taste phenylthiocarbamide (PTC)
The ability to taste phenylthiocarbamide (PTC) is a classic example of a physiological variation because it depends on specific chemical receptors on taste buds (a biochemical/functional process). It exhibits discontinuous variation because individuals inherit discrete genotypes resulting in distinct phenotypes (tasters or non-tasters) without any blending or intermediate tasting categories.

Step-by-Step Solution

1
Distinguish between morphological and physiological variations.
Morphological variations relate to physical appearance and anatomical structure (e.g., fingerprints, height, skin color). Physiological variations relate to internal function, biochemical processes, or behavioral reactions (e.g., blood groups, PTC tasting, tongue rolling).
The question specifically asks for a physiological variation.
2
Distinguish between continuous and discontinuous variation patterns.
Discontinuous variations fall into clear, distinct categories without intermediates (e.g., PTC tasting ability, ABO blood groups), while continuous variations show a complete spectrum of intermediate forms between extremes (e.g., height, weight).
The question requires a trait that shows discontinuous distribution.
3
Combine both criteria to identify the target trait.
PTC tasting is a physiological function (tasting chemical compound) and exhibits clear discontinuous categories (tasters vs non-tasters).
This satisfies both requested conditions simultaneously.

Key Concept

Human Morphological vs Physiological Variations and Patterns of Variation
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Topics

Human Morphological and Physiological Variations

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