From al715@yfn.ysu.edu Tue Jun 27 22:01:58 1995 Date: Wed, 28 Jun 1995 01:20:17 -0400 HOMOSEXUALITY: IT'S IN YOUR GENES (NOT JUST YOUR JEANS!) Part I Mitch King Charlottesville, VA WASHINGTON, 93 Jul 16--A group of researchers from the National Institutes of Health have discovered statistical evidence that one form of male homosexuality is genetically transmitted from mothers to their sons through the X chromosome. The study involved pedigree and DNA linkage analyses on 114 families of homosexual men. Subjects included 76 self-acknowledged homosexual men and their relatives over age 18 recruited through a Washington DC HIV clinic and local homophile organizations, and 38 pairs of homosexual brothers and their relatives recruited through advertisements in local and national homophile publications. Participants were white non-Hispanic (92%), African American (4%), Hispanic (3%), and Asian (1%). Sexual orientation was assessed by the Kinsey scales, and subjects rated themselves on four aspects of their sexuality: self-identification, attraction, fantasy, and behavior. Most of the men (average age 36) reported experiencing their first same-sex attraction by age 10, which was prior to the average age of puberty (age 12). For the first sample, (the 76 men from the Washington DC area), D. H. Hamer, S. Hu, V. L. Magnuson, N. Hu, and A. M. L. Pattatucci found that 13.5% of the brothers, 7.3% of the maternal uncles, and 7.7% of the sons of maternal aunts of homosexual men were self-acknowledged homosexuals--compared to the background rate of 2% which was an estimate obtained from 717 randomly selected males who were the subjects of previous research. Other significant findings were that 5.4% of the sisters of homosexual men were self-acknowledged lesbians (versus a 1% background rate), and 4.7% of the of the brothers of lesbians were self-acknowledged homosexuals (versus a 2% background rate). Homosexuality among fathers and all other types of paternally related relatives of the homosexual subjects was not significantly greater than the background rate. Although higher than the background rates, the observed rates of homosexuality in the maternally derived uncles and male cousins of gay men in the first sample were lower than would be expected for a simple Mendelian trait, so the researchers hypothesized that there might be at least two types of male homosexuality--one which was male-limited and maternally inherited versus one which was sporadic, not sex-limited, or not maternally transmitted. To test this hypothesis, Hamer et al. recruited the second sample--the 38 families in which there were two homosexual brothers. If their hypothesis concerning the existence of two types of homosexuality was correct, one would expect to see higher rates of male homosexuality in the maternally derived relatives of the second sample than in the first, and indeed, this is what was observed: 10.3% of the maternal uncles and 12.9% of the sons of maternal aunts of the homosexual brothers were, themselves, self-acknowledged homosexuals. Rates of homosexuality among the paternally derived male relatives were unchanged, or decreased compared to the first sample. For the linkage analysis, DNA from 40 pairs of homosexual brothers (38 from the sib- pair pedigree study, and 2 from the random sample) and from their available mothers and siblings was studied and typed for a series of 22 markers that span the X chromosome. A significant linkage between homosexual orientation and markers in a region of the X chromosome known as Xq28 was detected--33 sib-pairs (82.5%) had inherited the same genetic information at all five markers within this region, whereas 7 pairs (17.5%) showed differences at one or more markers. The probability that such coinheritance could occur by chance alone is much less than 1.0%. As the research report states, "it appears that Xq28 contains a gene that contributes to homosexual orientation in males". The 7 pairs (17.5%) of homosexual brothers who did not coinherit all of the Xq28 markers suggest that other factors, including nongenetic ones, play a role in determining sexual orientation. There was no significant evidence for linkage between sexual orientation and markers lying outside of Xq28, however, the researchers acknowledge that a much larger sample would be required to stringently eliminate all other regions from playing a role in sexual development in a small proportion of families. Reference: Hamer, D. H., Hu, S., Magnuson, V. L., Hu, N., and Pattatucci, A. M. L. "A Linkage Between DNA Markers on the X Chromosome and Male Sexual Orientation", Science, Vol 261, 321-327, 16 Jul 93. Science is published weekly by the American Association for the Advancement of Science, Washington, DC. Unrestricted reproduction or electronic transmission is authorized when due credit is given to the author. ---------------------------------------------------------------------- HOMOSEXUALITY: IT'S IN YOUR GENES (NOT JUST YOUR JEANS!) Part II Mitch King Charlottesville, VA WASHINGTON, 94 Dec--Two Canadian researchers have discovered a statistical relationship between the number of ridges on men's fingertips and homosexuality, contributing additional evidence to the theory that sexual orientation can be influenced by biological events that occur at conception or early in fetal life. Specifically, J. A. Y. Hall and D. Kimura of the University of Western Ontario examined the fingerprints of 66 homosexual and 182 heterosexual men, comparing the number of ridges on the index finger and thumb of the left hand with the number of ridges on the index finger and thumb of the right hand. If the number of ridges on the index finger and thumb of the left hand exceeds the number of ridges on the index finger and thumb of the right hand, one's fingerprints are said to exhibit leftward directional asymmetry. Hall and Kimura found such leftward directional asymmetry in the fingerprints of 30% of their homosexual subjects versus 14% of their heterosexuals. Sexual orientation was measured by having all subjects rank themselves, in terms of fantasy and experience, via the Kinsey scale. The number of ridges on the fingertips is largely determined at the moment of conception by genetics, subject to modification by local environmental factors (local hormone levels, etc.) up to the 16th week of fetal life. Only extensive mechanical damage alters the number of ridges after this time. According to Hall and Kimura, a significant statistical correlation between a prenatally determined characteristic such as one's fingerprints and an adult behavioral trait such as one's sexual orientation is consistent with previous research suggesting an early biological contribution to adult sexual orientation. Reference: Hall, J. A. Y. and Kimura, D. "Dermatoglyphic Asymmetry and Sexual Orientation in Men", Behavioral Neuroscience, Vol. 108, No. 6, 1203-1206, Dec 94. Behavioral Neuroscience is published bimonthly by the American Psychological Association, Washington, DC. Unrestricted reproduction or electronic transmission is authorized when due credit is given to the author. -------------------------- End of Attachment ----------------------------- -- ----------------- soc.support.youth.gay-lesbian-bi info --------------- *Articles should be posted normally or mailed to glb-youth@ucsd.edu *Moderator contact address: glb-youth-request@ucsd.edu *WWW home page and FAQ: http: //www.youth.org/ssyglb -- ______Tina M. Wood |"There is no scarcity of civil rights in America, \ /AL715@yfn.ysu.edu| only a scarcity of political leaders who will \ / twood@qrd.org | stand up for the rights of all citizens." \/ Cumberland, RI | --Robert Bray