The gift has no impact on the adjusted basis of the seller. Gain is calculated by the extent the amount realized (less selling expenses) exceeds the seller's adjusted basis.
See Treas. Reg. § 1.1001-1(e)(1)
The buyer's unadjusted basis is the greater of the amount paid or the transferor's adjusted basis increased by any gift tax paid (for determining a loss, the buyer's basis cannot be greater than the fair market value at the time of the transfer).
See Treas. Reg. § 1.1015-4(a)
