Left bias in pelvic vestiges in stickleback populations is used to infer which of the following about Pitx1?

• A. If the pelvic vestiges are larger on the left side in most stickleback in a population, the Pitx1 gene is probably involved in pelvic reduction.
• B. If the pelvic vestiges are larger on the left side, Pitx1 involvement is certain to be in hind limb development.
• C. The left-right bias in vestiges does not inform about Pitx1 involvement.
• D. Vestibule bias is related to other genes, not Pitx1.

Answer: (C)

The pattern we see here hinges on how Pitx1 actually influences pelvic development in sticklebacks. Pitx1 is known to affect hindlimb/pelvic formation through its regulation in pelvic tissue, and the pelvic reduction observed in many stickleback populations is linked to changes in Pitx1 expression in that region. But a left-right bias of pelvic vestiges across a population doesn’t reliably tell us whether Pitx1 is involved. Left-right asymmetry in development is governed by broader patterning mechanisms, and the presence of a bias on one side could arise from factors other than Pitx1’s pelvic function.

To infer Pitx1 involvement, you’d need direct evidence—such as showing Pitx1 is downregulated in pelvic buds of individuals with reduced pelvis, or demonstrating that altering Pitx1 expression or its pelvic regulatory elements reproduces the phenotype. So the population’s left-right bias in vestiges doesn’t by itself indicate Pitx1 involvement, making that option the best choice.