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Difficulty: MediumContinuous and Discontinuous Variation

Phenotypic traits exhibiting discontinuous variation, such as human ABO blood groups and tongue-rolling ability, are controlled by polygenic inheritance and show a continuous spectrum of intermediates modified by environmental factors.

Answer: Answer

Answer

The statement is False. Discontinuous variation features discrete, non-overlapping phenotypic classes governed by monogenic inheritance and is not modified by environmental factors.
The statement is false because discontinuous variation is characterized by clear-cut, non-overlapping phenotypic categories (such as blood types AA, BB, ABAB, and OO) controlled by single genes or single loci with few alleles (monogenic inheritance), operating independently of environmental influence.

Step-by-Step Solution

1
Identify the biological traits mentioned in the stem (ABO blood groups and tongue-rolling ability).
These phenotypic features are classic examples of discontinuous variation in humans.
Classifying the traits establishes the correct genetic framework.
2
Evaluate the genetic control and environmental influence described in the statement.
The statement attributes polygenic control and environmental modification to discontinuous traits.
Polygenic inheritance and environmental factors produce continuous variation (such as height or skin color), whereas discontinuous traits are monogenic and environment-independent.
3
Determine the validity of the statement.
Because the statement incorrectly pairs discontinuous traits with the characteristics of continuous variation, it is false.
A proposition containing contradicted biological definitions is false.

Key Concept

Genetic mechanisms of continuous vs. discontinuous variation
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Topics

Continuous and Discontinuous Variation

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