Final answer:
A study of maternal smoking during pregnancy and the DD genotype revealed that children whose mothers had smoked during pregnancy scored higher than children of nonsmokers in impulsivity, over-activity, and oppositional behaviour.
Step-by-step explanation:
A study found that children exposed to maternal smoking during pregnancy were more likely to exhibit impulsive, hyperactive, and oppositional behaviors compared to children of non-smoking mothers.
This association was linked to the presence of the DD genotype, suggesting that genetic predisposition may play a role in the behavioral effects of prenatal smoking exposure.