While glia generally play supporting roles, the communication between neurons is fundamental to all of the functions associated with the nervous system. In order to exhibit a recessive phenotype, an individual must be homozygous for the recessive allele.

A dominant allele always results in the dominant phenotype. Glia and neurons are the two cell types that make up the nervous system.

neuron — cells in the nervous system that act as interconnected information processors, which are essential for all of the tasks of the nervous system. recessive allele — allele whose phenotype will be expressed only if an individual is homozygous for that allele. nervous system — made up of billions of neurons and controls our thoughts, responses, and movements; divided into the central nervous system (CNS) and the peripheral nervous system (PNS). dominant allele — allele whose phenotype will be expressed in an individual that possesses that allele.