Twins are exceptional people. Only 4 out of every 1000 births produce a pair of identical (Monozygotic, or MZ) twins and another 4 result in same-sex fraternal (Dizygotic, or DZ) twins. Identical twins arise from a single egg and share the same genetic blueprint. Accordingly, differences between them must be due to differences in their environmental experiences. Fraternal twins arise from separate eggs and, like brothers or sisters from single births, share only 50% of their genes. Studying identical and fraternal twins thus allows us to estimate how genes and environment interact to influence character, strengths, vulnerabilities, and values. Twins as individuals are highly representative of people in general. The twins we study live in cities, in small towns, and on farms; some are wealthy, most are not; they are as diverse with respect to education, occupation, personality, interests, and family background as any representatvie sample of Minnesotans. Therefore, what we learn can be applied to Minnesotans in general.
We are Interested in Parents, Too
While twins occupy a special postion in science, their parents are an extremely important part of our study as well. Because parents and children share 50% of their genetic blueprint, we are interested in knowing how similar or different parents and their adolescent children are in important behavioral and intellectual characteristics. We are also interested in knowing how parents' attitudes, experiences, and relationships influence their children's behavior and development.