A genetic characteristic of an individual is any trait that can be attributed to a hereditary cause, coded for in inherited DNA. Any other trait is derived from environmental causes, either while within the womb or outside of it. It can be very difficult to determine if a characteristic is genetic, congenital but not genetic or acquired after birth.
Generally, any characteristic that appears in one family for several generations is suspected to have a genetic cause. Some genetic characteristics are fairly well-known and uncontroversial. These include such benign traits as hair color, eye color, attachment of earlobes, hair texture and freckles. However, just because a trait has a genetic basis does not mean that a person with that gene will have that characteristic.
Among the genes that cause various characteristics in individuals, some are dominant and some are recessive. For instance, if a person carries genes for brown eyes from her mother and genes for blue eyes from her father, her eyes will normally be brown. This is because the genes for brown eyes are dominant over the genes for blue eyes. When both are present, the maternal genes have more influence. This dominance is usually not total, and some compromise between opposing genes is often the result.