[New approach in the explaining of the Morgan Law in genetics teaching].

Using the model of broad and narrow way, the paper introduces a new approach in the explaining of a few basic concepts in the Morgan Law. The paper introduces a thorough inquiry into the applying condition of the three-factor crosses, and finds the source of the difference between the crossover frequency (F(C)) and recombination frequency (F(R)) of the non-adjacent factors in the three-factor crosses in Neurospora crassa.