What does the suffix -zygous mean? (Genetics)

Having a zygotic constitution of a specified kind:heterozygous.

relating to the word zygous

i.e. heterozygous

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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i think the answer would d