If left pelvic vestiges are larger in a population, what does this suggest about Pitx1's role?

• A. Pitx1 is not involved.
• B. Pitx1 is involved in pelvic inversion.
• C. Pitx1 is probably involved in pelvic reduction.
• D. Pitx1 is involved in immune response.

Answer: (C)

The size of the pelvic vestiges reflects how much pelvic development occurs in that region, and Pitx1's activity there governs that development. In sticklebacks, reduced Pitx1 expression in the pelvic area leads to pelvic reduction, while normal or stronger expression supports fuller pelvic structures. So if a population shows larger left pelvic vestiges, it suggests that pelvic reduction is less pronounced in that population, which points to Pitx1 being involved in reducing the pelvis. This interpretation fits the pattern that changes in Pitx1 regulation can drive the observed pelvic-size differences between populations. It doesn’t align with roles in immune function or in pelvic inversion.