[Campbell Biology P.536] The text distinguishes between two ways phenotypic differences vary... | Practice Question

The text distinguishes between two ways phenotypic differences vary. Which of the following best describes "gradational" phenotypic differences as opposed to "either-or" differences?

  • A: "Gradational" traits are determined by a single gene locus, while "either-or" traits are influenced by multiple genes.
  • B: "Gradational" traits show distinct categories (e.g., purple or white flowers), while "either-or" traits vary along a continuum (e.g., height).
  • C: "Gradational" traits typically result from the influence of multiple genes, while "either-or" traits are determined by a single gene locus.
  • D: "Gradational" traits are only observable in molecular form, while "either-or" traits are always visible phenotypic differences.

Explanation

The text explains: 'Some heritable phenotypic differences occur on an 'either-or' basis, such as the flower colors of Mendel's pea plants... Characters that vary in this way are typically determined by a single gene locus, with different alleles producing distinct phenotypes. In contrast, other phenotypic differences vary in gradations along a continuum. Such variation usually results from the influence of two or more genes on a single phenotypic character.'