Sexual Orientation - Research Article from Macmillan Science Library: Genetics

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Twin and Family Studies

Twin studies are a classic tool for examining the role of genes. Twins brought up together share a similar environment. Monozygotic twins share all their genes, while dizygotic twins share only half their genes. Early twin studies by Franz Kallmann in 1952 and Leonard Heston in 1968 reported that if one monozygotic twin was homosexual, there was a greater chance the other twin would be homosexual. The likelihood of this was greater than for dizygotic twins. These studies were potentially biased. They recruited homosexual subjects and had relatively small sample sizes. Recent twin studies have examined all twins in a community without regard to sexual orientation, providing large, less biased sample sizes. In 2000 Kenneth Kendler and colleagues evaluated genetic and environmental factors in a large U.S. sample of twin and nontwin sibling pairs. Sexual orientation was classified as heterosexual or nonheterosexual (bisexual or homosexual) and...

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This section contains 1,063 words
(approx. 4 pages at 300 words per page)
Buy the Sexual Orientation Encyclopedia Article
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Macmillan Science Library: Genetics
Sexual Orientation from Macmillan Science Library: Genetics. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.
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