If the same base pairs are used to code for all organisms, why is there so much variation among organisms

The correct answer is due to the change in the sequence of codons of genes as a result of recombination.

Explanation:

Four types of nucleotide base pairs namely adenine, cytosine, guanine and thymine are present in the DNA sequence which controls the trait of an organism as they encode "proteins."

These base pairs are read by the ribosome during translation in the form of triplet known as codons. It is the sequence of these codons which directly controls the morphological and physiological trait of an organism.

These codons are present in the genes - a coding segment of DNA on chromosomes which during meiosis I undergo recombination via crossing over between homologous chromosomes which results in the change in the order of these codons thus changing the amino acid sequence and hence proteins. This is the basis of genetic diversity.

Thus, due to the change in the sequence of codons of genes as a result of recombination is the correct answer.

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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answer; i do believe that the correct answer is; ///mendelian genes are at specific loci on the chromosome and, in turn, segregate during meiosis;