2 mishnayot: 1 – A first-born son receives a double-inheritance from his father’s property, though not his mother’s property. (Note: The potential modern will complications (which are largely avoidable, but still) would be in Israel, not elsewhere). But improvements to the property after the father’s death and other kinds of property would not be counted as a double portion. Nor a woman receiving her ketubah, nor daughters receiving mezonot, nor a yavam. 2 – During a jubilee year (yovel), the land reverts, but there are exceptions — including the double-portion of the first-born. Note the Gemara’s interpretation of this mishnah — a husband’s inheritance of the wife’s property may not revert either, or if it does, perhaps he wouldn’t be compensated for it. But this inheritance, according to the Gemara, becomes her family’s ancestral plot for burial, and not some other land.