Opposite Personalities and Appearances of Twins

"Identical" DNA: Not Always Identical

• Identical twins are conceived from one egg that is fertilized by one sperm, the cells replicating and splitting off to form another entity. While it is commonly believed that identical twins share the exact same DNA, research conducted at the University of Alabama Birmingham by geneticist Carl Bruder demonstrates that in some cases, one twin's DNA will differ slightly from the other twin's DNA. This small difference can affect how an individual's physical and personality traits develop over time. While identical twins frequently share many physical characteristics, it is possible for features to be different. Personalities can also reflect opposite tendencies, perhaps due to the modest differences in genetic composition.

Fraternal Twins and Mirror-Image Twins

• Fraternal twins are conceived from two separate eggs fertilized by two separate sperm to form two individual embryos. Fraternal twins share only approximately 50 percent of DNA sequence variations, contributing to the more apparent differences between their physical and personality qualities. Fraternal twin gender combinations can be male-male, female-female or male-female, increasing the probability for both physical and behavioral differences. Studies conducted at The Krembil Family Epigenetics Laboratory in Ontario show that differences in personality traits are higher for different-sex fraternal twins than identical or same-sex fraternal twins. Approximately 25 percent of identical twins are mirror-image twins, forming from a single fertilized egg. The split occurs late, more than a week after conception. In the case of mirror-image twins, reverse asymmetric features are known to develop. It is possible for these twins' personalities and behaviors to reflect opposite tendencies as well.

Environmental Factors

• The environment in which twins grow up can also affect the outcome of behavioral characteristics. In some cases, identical twins grow up in completely different environments with different sets of parents yet, as adults, they reflect highly similar behavioral traits. It is possible, nonetheless, for twins to develop differently based on even slight variations in childhood environments. Perhaps one twin spent more time in a baby swing as an infant and one was held more often or one twin spent more time with the father and the other twin was with the mother more frequently. These minor differences have the ability to influence the personality development of each individual twin.

Parental Awareness and Consideration

• As a parent of twins, it is important to recognize that each child is an individual with characteristics, interests and development differences of his own. Christina Baglivi Tinglof, author of four books on parenting twins and mother to twins herself, emphasizes the value of treating your twins as separate individuals in order to provide an optimal environment for your twins' character development. It is beneficial to acknowledge and nurture the differences you perceive in each twin's behavior and personality so they can grow up feeling confident as individuals.