Now, any parent with a mutation that results in extra female offspring would be favored.

现在任何发生基因变异的父母都会因有雌性后代而会受到优待。

They've been modified so that the female offspring they produce will die before they hatch from their eggs and grow big enough to bite people.

经过改造后，它们交配后产生的雌性后代会在从卵里孵化出来之前死亡，不会生长到足以叮咬人的程度。