Red-green colour blindness is the commonest inherited colour vision defect. Its inheritance pattern and genetic basis are best described as:

• A X-linked recessive mutations affecting the L- and M-cone opsin gene cluster on the X chromosome ✓
• B Autosomal dominant mutation affecting the S-cone opsin gene on chromosome 7
• C Mitochondrial inheritance affecting retinal ganglion cells
• D Autosomal recessive mutation of rhodopsin on chromosome 3

Explanation

The genes encoding long-wave (red, L) and middle-wave (green, M) cone opsins lie in a tandem array on Xq28, and defects in this cluster produce protan and deutan defects, typically inherited as X-linked recessive traits, explaining the marked male preponderance. The S-cone (blue) opsin gene is on chromosome 7 and its defects are rare and autosomal dominant. Rhodopsin mutations cause retinitis pigmentosa, not colour blindness.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.