A geneticist analyzed the phenotypic distribution of two traits in a population of fruit flies (*Drosophila melanogaster*): wing length measured in millimeters and eye color (red versus white). When cultures were reared across a range of ambient temperatures, the wing lengths across the population formed a smooth spectrum whose mean value shifted significantly with temperature changes. In contrast, eye color consistently segregated into two discrete, non-overlapping categories in predictable Mendelian ratios regardless of rearing temperature. What does this observation indicate regarding the genetic control and environmental sensitivity of these two traits?
- Wing length is polygenic and influenced by environmental factors, whereas eye color is monogenic and unaffected by temperature variations.Answer
- BWing length displays discontinuous variation regulated by a single gene, whereas eye color demonstrates continuous variation governed by multiple additive genes.
- CBoth traits are polygenic, but wing length shows codominance while eye color undergoes thermal inactivation at higher temperatures.
- DWing length is governed strictly by temperature without genetic contribution, while eye color is caused by a chromosomal aberration.
Answer
Wing length is polygenic and influenced by environmental factors, whereas eye color is monogenic and unaffected by temperature variations.
Continuous variation (such as wing length) is quantitative, controlled by multiple additive genes (polygenic inheritance), and readily modified by environmental conditions such as temperature. Discontinuous variation (such as eye color) is qualitative, controlled by one or a few major genes (monogenic inheritance), and produces distinct, non-overlapping categories that remain stable despite environmental fluctuations.
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Key Concept
Polygenic vs Monogenic Control in Continuous and Discontinuous Variation
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