Final answer:
The study by Brody et al. (2009) found that an intervention designed to improve family communication had an impact on boys with a long allele of the 5-HTTLPR gene, indicating the interplay of genetics and environmental interventions.
Step-by-step explanation:
An intervention study that aimed to improve family communication and cohesion between parents and their sons found that genetic factors play a role in how individuals respond to their environment. Specifically, the serotonin transporter gene (5-HTTLPR) was examined in this context. The study referenced, Brody et al. (2009), revealed that the intervention had an impact on boys with a long allele of the 5-HTTLPR gene. This finding echoes similar research that explores the gene-environment interaction, suggesting that certain genetic makeups can influence the effectiveness of psychological and social interventions.