[Campbell Biology P.596] Which statement best explains the evolutionary reduction of ventral... | Practice Question

Which statement best explains the evolutionary reduction of ventral spines in lake stickleback fish, as described in the text?

  • A: Changes in regulatory noncoding DNA (like the Pel enhancer) altered Pitx1 gene expression in specific tissues, leading to reduced spine development.
  • B: Direct mutations occurred within the Pitx1 gene's protein-coding sequence, leading to a non-functional protein.
  • C: The entire Pitx1 gene was lost from the genome of lake sticklebacks.
  • D: Increased calcium availability in lakes allowed for the formation of weaker spines, which were then selected against.

Explanation

The text clarifies that the reduction in spines in lake sticklebacks is due to changes in how the Pitx1 gene is expressed, specifically through alterations in the Pel enhancer a noncoding DNA region , rather than changes to the Pitx1 gene's DNA sequence itself. This leads to targeted morphological changes.