4.Individuals crossing exclusively within the same population produce more progeny than those crossing in both directions and thereby use up some of their gametes for the production of inviable hybrids.
完全在同一种群内进行杂交
个体比以两个方向进行杂交
个体繁殖后代要多,因此为了产生无生机
杂种,就要消耗掉一些配子。