In some instances, humans breed animals that are close relatives to produce desired traits. this is called

A large biological molecule composed of subunits known as nucleotides ... Evolution consists of changes in the heritable traits of a population of ... In some cases mutations result in the organism possessing these altered traits to ... The intentional breeding of organisms with desirable traits in an attempt to produce offspring ..

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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substitution is the answer in this case