This family trait that skips a generation comes from an autosomal recessive trait or as Mendel called as hidden non-dominant trait. Offsprings have a dominant and recessive trait which comes from both parents. Recessive trait appears only when two offspring with same recessive trait blends. This happens in self-fertilization. In the human population, marriage is prohibited between offsprings, thus having recessive trait is only imminent when cousins are married.
