Why does the word trait appear in parenthesis in sentence 1?

As trait being the synonym for characteristics, it appears in parenthesis in sentence 1.

Explanation:

Heredity is a process through which traits pass from parents to their children. Traits are very important because it helps in describing patterns of behavior for a long span of time.

Five most important personality traits are as follows, consciousness, openness, neuroticism, extraversion, agreeableness. There are certain difference between traits as well as skills , traits are those which a child derive from his or her parents and skills are those which a person develops in lifetime.