Since crossing over can occur during the first meiotic division, it does allow for some genetic variation in the offspring. 在第一次减数分裂的过程中可以发生交换现象，因而在后代中有遗传变化。
It followed a normal course up to first meiotic metaphase when it inexplicably failed. 它按正常减数分裂过程进行到第一次减数分裂中期后就莫名其妙地停止了。
