Where a deed purports to convey a greater interest than the grantor was at the time possessed of, any after-acquired interest of such grantor, to the extent of that which the deed purports to convey, inures to the benefit of the grantee. But if the spouse of such grantor joins in such conveyance for the purpose of relinquishing dower or homestead only, and subsequently acquires an interest therein as above defined, it shall not be held to inure to the benefit of the grantee.
Iowa Code § 557.4