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Developmental Mechanisms, Monozygotic Versus Dizygotic Twins, Similarities And Differences Between Monozygotic Twins, Amazing Twin SimilaritiesConclusion

Twins are siblings carried together in the womb and born at the same time. Similarities and differences between twins can be used to answer questions about the role genes and the environment play in the development of traits such as personality, intelligence, and susceptibility to disease. While results from any single pair of twins cannot provide conclusive answers to such questions, the study of large numbers of twin pairs allows researchers to draw conclusions about inheritance with a significant degree of confidence.

Twin studies provide a unique approach to investigating the determinants of a disease or condition. A single twin study cannot absolutely determine the importance of genetic or environmental factors. However, the twin study method, in combination with other approaches, can be a powerful tool for unraveling the causes of disease.

Caroline M. Tanner

and Richard Robinson


Bouchard, T. J., et al. "The Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart." Science 250 (1990): 223-228.

Segal, Nancy L. Entwined Lives: Twins and What They Tell Us about Human Behavior. New York: Plume, 2000.

Wright, Lawrence. Twins: And What They Tell Us about Who We Are. New York: John Wiley & Sons, 1997.

Internet Resource

Minnesota Twin Family Study. University of Minnesota. <http://www.psych.umn.edu/psylabs/mtfs/default.htm>.


  • To estimate the relative contributions of genes and environment to the cause of disease by comparing MZ to DZ concordance;
  • To investigate environmental determinants of etiology in discordant twin pair studies;
  • To investigate environmental influences on disease course in concordant twin pair studies;
  • To characterize "presymptomatic" or "at risk" states by studying the unaffected twins in discordant pairs.

Additional topics

Medicine EncyclopediaGenetics in Medicine - Part 4