Associated means correlated with.. I gave you an analogy of chromosomes being associated with physical traits.

>>How are chromosomes associated with behaviour?

The same way they're associated with physiological traits. Personality traits are not all learned. There is a large genetic effect on behaviour. There is plenty of scientific evidence for this.

>>Is picking one's nose a "behavioual trait", for example?

How am I supposed to know that? Why would any researcher conduct a study to uncover that?