Traits which exhibit continuous phenotypic variation are typically determined by this inheritance form

The correct option is polygene inheritance.

To understand why polygene (or polygenic) inheritance is responsible for traits that show continuous phenotypic variation, we can break down the genetic mechanisms step-by-step:

1. Continuous Phenotypic Variation: Traits that exhibit continuous variation do not fall into neat, distinct categories (like wrinkled vs. smooth peas). Instead, they show a wide, unbroken range of phenotypes. Examples in humans include height, skin color, and weight. When plotted, these traits typically form a bell-shaped curve (normal distribution) in a population.

2. Polygenic Inheritance: This form of inheritance occurs when a single phenotypic trait is controlled by the cumulative effects of multiple, independent genes (polygenes). Each gene has a small, additive effect on the final phenotype. As the number of genes controlling the trait increases, the number of possible phenotypic combinations increases exponentially, smoothing out the differences between categories and leading to a continuous spectrum.

3. Why other options are incorrect:
- Incomplete dominance results in an intermediate phenotype in heterozygotes (e.g., pink flowers from red and white parents), typically producing distinct, discrete categories rather than a continuous range.
- Multiple-allele inheritance involves more than two alleles for a single gene locus (like ABO blood types), which still results in distinct qualitative categories (Type A, B, AB, or O).
- Sex-linked inheritance refers to genes located on sex chromosomes, which does not inherently result in a continuous distribution of a trait across a population.