The Gigabyte Z270X-Gaming 7 comes with three PCI Express 3.0 x16 slots and three PCI Express 2.0 x1 slots. There are also one M.2 slot supporting both PCI Express 3.0 x4 and SATA-600.
The two first PCI Express x16 slots work on x16/x0 and x8/x8 configurations, which means the first slot work at x16 if the second one is unused, but it it is occupied, they will both work at x8.
The third PCI Express 3.0 x16 slot works always at x4 speed and, according to the manufacturer, shares its lanes with the second M.2 slot.
The motherboard supports CrossFire with up to three and SLI with two video cards.
The PCI Express x16 slots are covered by stainless steel shields, that work as a shield against interference, and also improving mechanical strength of each slot.
Figure 2: slots