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Difficulty: MediumHuman Morphological and Physiological Variations

A medical survey categorizes human traits according to their biological nature (morphological versus physiological) and their population distribution pattern (continuous versus discontinuous). Which of the following pairings correctly matches a physiological trait exhibiting discontinuous variation with a morphological trait exhibiting continuous variation?

  1. Ability to taste phenylthiocarbamide (PTC) and adult body heightAnswer
  2. B
    Human ABO blood group system and presence of free earlobes
  3. C
    Fingerprint arch patterns and human skin pigmentation shade
  4. D
    Systolic blood pressure and tongue rolling ability

Answer

Ability to taste phenylthiocarbamide (PTC) and adult body height
The ability to taste phenylthiocarbamide (PTC) is a physiological trait involving chemical receptor function that splits the population into clear qualitative classes (tasters and non-tasters, showing discontinuous variation). Adult body height is a structural feature (morphological trait) influenced by multiple gene pairs and environmental factors, producing a continuous spectrum of quantitative values.

Step-by-Step Solution

1
Classify traits by biological type (morphological vs. physiological)
PTC tasting ability and blood pressure are physiological traits (functional/biochemical), whereas fingerprint patterns, earlobe attachment, and height are morphological traits (physical form/structure).
Physiological traits pertain to internal function and biochemistry, whereas morphological traits pertain to physical appearance and body form.
2
Analyze distribution patterns (continuous vs. discontinuous)
PTC tasting is discontinuous (clear-cut categories without intermediate forms). Adult height is continuous (controlled by polygenes and modified by environment, forming a smooth gradient).
Discontinuous traits are typically monogenic with distinct categories, while continuous traits are polygenic with a range of intermediate values.
3
Match the required pairing conditions
The pairing of PTC tasting ability (physiological, discontinuous) with adult body height (morphological, continuous) fulfills both conditions perfectly.
This is the only pair containing a physiological discontinuous trait alongside a morphological continuous trait.

Key Concept

Classification of Human Morphological and Physiological Variations by Pattern of Inheritance
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Topics

Human Morphological and Physiological Variations

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