Definition: Methods of detecting genetic etiology in human traits. The basic premise of twin studies is that monozygotic twins, being formed by the division of a single fertilized ovum, carry identical genes, while dizygotic twins, being formed by the fertilization of two ova by two different spermatozoa, are genetically no more similar than two siblings born after separate pregnancies. (Last, J.M., A Dictionary of Epidemiology, 2d ed)
for general design, methodology, economics, etc of twin studies; main headings DISEASES IN TWINS; TWINS; and specifics are also available; do not confuse with the Publication Type TWIN STUDY
