For example, the tendency towards introversion can be measured almost from infancy, before environmental factors have had much chance to influence personality. However, this genetic tendency doesn't doom one to a life of social introversion. Many environmental factors come into play. If, because of career demands, for example, the person feels a strong need to overcome his innate shyness, he can do so. Also, personality is subjective.
Personality varies depending on who observes the individual.
I was surprised at the outcome. My mother only rated me the same as I did 3 out of 4 times. My brother rated my personality almost exactly opposite of my own rating of it. My point is that variation between individuals is due not only to a combination of genetic and environmental circumstances, but to the circumstances the individual is in from moment to moment. A clone, then, while he or she might be an exact genetic match, will never be a true replica of its parent.