What fraction of the energy from one trophic level carries up to the next trophic level?

One-tenth .

Explanation:

Energy flow in an ecosystem is is determined by two basic laws of thermodynamics; the first law of thermodynamics and second law of thermodynamics.According to the second law of thermodynamics, there is a gradual decrease in energy at successive trophic levels.It is so because at each transfer, about 80-90% of energy available at lower trophic level is used to overcome its entropy and to perform metabolic activities.Only one-tenth (10%) of the total energy is carried up to the next trophic level.The law governing the retaining of only 10% of chemical energy at each trophic level is called ten percent law.

They create genetic variations