What type of cross is used to determine if an individual with the dominant form of a trait is homozygous or heterozygous?

For a certain trait is unknown and an organism that is homozygous recessive for that trait 

Neurotransmitters are messengers responsible for communication between neurons. they are released from synaptic vesicles and are received by receptors.  the communication is referred to as neurotransmission. the following statement is true about neurotransmitters: a. they're stored in synaptic vesicles in the axon.