A mutation disrupting HOX gene expression specifically affects segmental identity of vertebrae. Thoracic vertebrae 'transformed' into cervical identity (homeotic transformation) would most likely result from a mutation in which class of genes?

• A HOX group A genes ✓
• B PAX genes
• C SHH signalling pathway
• D Notch–Delta signalling

Explanation

HOX genes of the HOXA cluster (and the paralogue groups) specify the rostrocaudal identity of vertebrae along the axial skeleton. Loss-of-function mutations cause 'anterior homeotic transformations' where posterior segments adopt the identity of more anterior (rostral) segments. PAX1/PAX9 are involved in vertebral body formation and sclerotome differentiation but not segmental identity per se. SHH specifies ventral neural tube and sclerotome induction. Notch-Delta regulates somite segmentation (somitogenesis clock).

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.