Final answer:
Psychological researchers study genetics to understand biological factors in human behavior. Genes affect temperament and psychological disorders.
Step-by-step explanation:
Psychological researchers study genetics in order to better understand the biological factors that contribute to certain behaviors. Genes affect more than our physical characteristics, as they are also associated with temperament and psychological disorders. Researchers use twin and adoption studies to investigate the relative importance of genes and environment for the expression of a given trait.