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Difficulty: HardContinuous and Discontinuous Variation

Human skin color exhibits continuous variation because it is governed by polygenic inheritance with additive gene action, allowing environmental exposure to modify phenotypic expression along a continuous spectrum, whereas discontinuous traits like the ABO blood group system are controlled monogenically and are exempt from environmental modification.

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Answer

True. Continuous variation is characterized by polygenic inheritance and environmental influence, whereas discontinuous variation is governed by monogenic inheritance without environmental modification.
The statement accurately presents biological facts: continuous traits like skin color are polygenic and influenced by environmental factors such as sunlight, whereas discontinuous traits like ABO blood groups are controlled by a single gene locus and remain completely unaffected by the environment.

Step-by-Step Solution

1
Analyze the genetic basis of continuous variation in phenotypic traits.
Traits showing continuous variation (such as skin color, height, and body mass) are controlled by multiple independent gene pairs acting additively (polygenic inheritance).
Polygenic inheritance creates a continuous distribution of phenotypes rather than discrete categories.
2
Assess the role of environmental factors on continuous versus discontinuous traits.
Environmental exposure (such as sunlight altering melanin production for skin color or nutrition altering height) shifts phenotypes along a smooth gradient. Discontinuous traits (such as ABO blood groups or tongue rolling) are genetically fixed and immune to environmental modification.
Differentiating environmental influence helps distinguish continuous variation from discontinuous variation.
3
Evaluate the genetic control mechanism of discontinuous traits.
Discontinuous traits are inherited monogenically (or via a single gene locus with major alleles), leading to distinct, non-overlapping phenotypic classes.
Single-gene inheritance prevents intermediate phenotypic gradations from forming in populations.
4
Determine the validity of the complete statement.
Both assertions regarding genetic mechanism (polygenic vs monogenic) and environmental sensitivity (modifiable vs exempt) are scientifically accurate, making the statement True.
The contrast drawn between skin color and ABO blood group inheritance correctly reflects the mechanisms of biological variation.

Key Concept

Polygenic vs Monogenic Control of Continuous and Discontinuous Variation
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Topics

Continuous and Discontinuous Variation

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