Which one of the following describes an epigenetic modification? A point mutation in the coding sequence of a gene. A deletion in the regulatory region of a gene. A nonsense mutation in the coding region of a gene. A methyl group bound to DNA inhibits transcription of a gene.

Explanation:

A methyl group bound to DNA inhibits transcription of a gene describes an epigenetic modification

Epigenetic modifications include: histone modifications and methylation

Methylation is the main cause of gene silencing for example methylation at lysine residue of histone protein, H4 leads to gene repression

Small silencing RNA molecules are of two types: micro RNA (miRNA) and small interfering RNA (siRNA)

miRNA directs degradation of target mRNA when makes perfect complementary while suppress mRNA translation when makes partial or imperfect complementary

siRNA primarily mediates degradation of target RNA

Explanation:

1. Epigenetic modification: Those changes which do not involve the alterations in the sequence of DNA, means there in no change in DNA sequence, like addition, deletion or such other type of changes in the sequence of nucleotide do not occur

2. Epigenetic describes any  such type of modification of chromosome( which do not change the sequence of nucleotide), especially histone modifications, and these changes may be heritable or not  or associated with a phenotype.

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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the answer is 100% density i've answered this question before and done the quiz myself.