| twin pregnancy | A pregnancy that may result from the fertilization of two separate ova or of a single ovum. See: twin. Synonym: bigeminal pregnancy. (05 Mar 2000) |
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| twin studies | Methods of detecting genetic aetiology in human traits. The basic premise of twin studies is that monozygotic twins, being formed by the division of a single fertilised 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. (12 Dec 1998) |
| twin study | A method of detecting genetic causes in human traits and genetic factors in behaviour using sets of twins. (12 Dec 1998) |