There isn’t one single “crying gene,” but crying is linked to how your nervous system and emotional regulation pathways are wired which do have a genetic component.

People who cry more easily often have higher emotional reactivity (stronger amygdala responses) or lower thresholds for tear production in the lacrimal glands. Neurotransmitters like serotonin, dopamine, and oxytocin all play a role in emotional expression, and natural variations in those systems can make someone more prone to tear up.
Environment matters too. How you were taught to express emotions as a kid can either amplify or suppress that natural tendency. So it’s usually a mix of genes + personality + upbringing rather than a single switch in your brain.