Genez produced some wonderful guns. Like many makers in that period, mid 1800s, he made conversions from other detonation forms to a newer one, as well as furnishing complete guns. Your gun seems to be a center fire breechloader converted from a pinfire. It would be interesting to see the proofmarks. Many of the Genez marked guns were of English origin, so I'd guess your's is , too. Underlever locking is typical English of the period. Many of the Genez guns were "finished up" here with fine workmanship and the best engravers of the time. I have seen Genez marked muzzleloaders , pinfires, centerfires, etc. I do not recall seeing a Genez hammerless gun. Some guns have gold inlays .
Your gun has an unusual looking extractor, in that it goes around much of the shell circumference. I'd guess the market value in higher three figures or lower 4 figures, but think it is worth much more as a keepsake.
