Mo. Rev. Stat. § 474.040: Collaterals of half blood inherit, how.

When the inheritance is directed to pass to the ascending and collateral kindred of the intestate, if part of the collaterals is of the whole blood of the intestate, and the other part of the half blood only, those of the half blood shall inherit only half as much as those of the whole blood; but if all collaterals are of the half blood, they shall have whole portions, only giving to the ascendants double portions.