In humans, the ability to roll your tongue is dominant while not being able to roll your tongue is recessive. The gene for tongue rolling ability is represented by the letter R. Johnny can roll his tongue.

What are Johnny's possible genotypes?

Rr Rr . becaUse of science you so dunb arshole

come on how u  not know this

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.