Iowa's antilapse statute (Iowa Code sec. 633.273) provides that if a devisee dies before the testator, leaving issue who survive the testator, the devisee's issue inherit the property devised unless the terms of the will indicate to the contrary. Huh?
What this means, if you want person A to receive property, but only if they survive you, then you need to specifically require that they must survive you in order to receive their inheritance. Otherwise, if you don't, their children will inherit what you intended to go to their parent.
A recent case of In re: Delmege Estate, the Iowa Court of Appeals addressed the application of the Iowa antilapse statute. In that case, five siblings were named as devisees under a will, but one of the siblings predeceased the testator leaving two daughters. The Court found that if the decedent didn't want his nieces to inherit, he could have easily crafted his will for that purpose by including a survivorship clause. There is a presumption that the testator knew about the antilapse statute. (I wonder if the DIY wills fully address this issue.)