https://www.frontiersin.org/articles/10.3389/fpsyg.2020.01521/full?report=reader
Here the authors study the serotonin transporter in a Han Chinese population. They preface the article by saying:

When a harmful action was performed for the noble goal of benefitting the majority, even though such action bore an inevitable sacrifice, individuals with higher anxiety were found to release themselves and show more willingness to become the driving force of this type of harmful behaviors. However, when the harm was not inevitable and could be explicitly attributed to the agents, individuals with higher anxiety were reluctant to administer

They find that sesrotonin transporter gene was associated with decision making in moral dilemnas. Emotional effects (higher anxiety) of the P trait gene had more of a role than it did for those with non-P trait gene such that those with P trait gene were reluctant to sacrifice someone.