Like other osmoregulatory animals that live in marine environments, sharks maintain tissue concentrations of sodium, potassium, and chloride that are hypoosmotic to the seawater. In contrast to the bony marine fishes, however, sharks do not need to drink seawater. Why

Shark is hyperosmotic relative to sea water.

Explanation:

The sharks that live in the marine environment do not need to drink sea water unlike others.

This is because the concentration of the urea and oxide is trimethyl amine gets deposited in the tissues of the shark which is hyper osmotic condition to the outside environment( sea water).

There is an adequate amount of potassium, sodium and chloride in the body of shark.

This is how the shark maintains the osmoregulatory mechanism in marine environment.

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.