When you are exposed to sunlight for a long time, your skin, which otherwise appears normal, gets heavily tanned. what could be the reason?

a. the genes for melanin pigmentation remain turned on and prepare more melanin than usual to protect the skin from photo-damage when it is exposed to sunlight for long time.
b. the genes for melanin pigmentation remain turned off and synthesize more melanin than usual to protect the skin from photo-damage when it exposed to sunlight for a long time.
c. the genes for melanin pigmentation are switched off to stop the synthesis of melanin.

A. The genes for melanin pigmentation remain turned on and prepare more melanin than usual to protect the skin from photo-damage when it is exposed to sunlight for long time. 

Melanin is a pigment that gives the human skin, hair, and eyes their hue. Moreover, with this pigment it helps the individual against sun's rays or UVR that damages the skin tissue if in contact for a long period of time.  

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Proteins are the workhorses of the cell, controlling virtually every reaction within as well as providing structure and serving as signals to other cells. proteins are long chains of  amino acids  , and the exact sequence of the amino acids determines the final structure and function of the protein. instructions for that sequence are encoded in  genes  . to make a particular protein, a messenger ribonucleic acid (mrna) copy is made from the gene (in the process called  transcription  ), and the mrna is transported to the  ribosome  . protein synthesis, also called  translation  , begins when the two ribosomal subunits link onto the mrna. this step, called initiation, is followed by elongation, in which successive amino acids are added to the growing chain, brought in by transfer rnas (trnas). in this step, the ribosome reads the  nucleotides  of mrna three by three, in units called  codons  , and matches each to three nucleotides on the trna, called the anticodon. finally, during termination, the ribosome unbinds from the mrna, and the  amino acid  chain goes on to be processed and folded to make the final, functional protein