Most single gene defects that affect human behavior do so

Most single gene defects that affect human behavior do so
  A. as a primary effect of the gene.
  B. through their action on the structure, development, or function of the nervous system.
  C. by affecting muscle metabolism.
  D. by having only subtle effects on the nervous system.
  E. by gene action that takes place only in the adult stage of life.

Question 2

Huntington disease is
  A. a model of a multifactorial trait, controlled by several genes.
  B. inherited as an X-linked dominant trait.
  C. a disease with onset in early childhood.
  D. one that produces no significant changes in brain cells.
  E. a model of a single gene defect affecting behavior.