It Has Been Predicted That Genes May Be Involved in Smoking

It has been predicted that genes may be involved in smoking initiation and/or current smoking behavior. Previously, large twin and family studies have provided evidence of this and an estimate of heritability (genetic contribution) of 37-55% for initiation and 46-59% for current smoking, depending on gender. A large group of researchers from several institutions composed a pathway- or-systems-based series of studies including SNP analysis, cellular location and protein interaction, replication with other samples, statistical analysis, and bioinformatics. What is a likely result?

A) The study is unlikely to produce meaningful results because it is too diffuse in its methods.
B) The samples used also correlate with behaviors like depression, often associated with smoking, and they may be finding depression-associated genes.
C) Two specific genes, one for a transporter protein and one for an opioid receptor, are clearly shown to be causative in all members of each sample.
D) A group of genes that tend to code for proteins with similar biological function have been identified to contribute significantly.
E) Genome-wide association studies are of no practical use in studying human behaviors.