Term Paper: Resolve Conflicting Evidence That Male

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[. . .] In addition, a simple genetic explanation of homosexuality is difficult to envision, considering the argument that the selective pressure for homosexuality would not be strong. Homosexuals are likely much less likely to reproduce than are heterosexuals, thus leading to strong selective pressures against a simple Mendelian gene that controls homosexuality (Rice et al., 1999). Despite this, several theories have been proposed to account for the presence of gay genes, including the postulation that gay genes may help promote the reproductive success of the siblings of gay people (Bailey, 2003).

As noted earlier, there are often a number of methodological problems that undermine the existing evidence that sexual orientation has a genetic basis. In samples where participants are recruited using homophile publications, the concordance rates for sexual orientation among monozygotic and dizygotic twins are higher than when samples are taken from the general population. This can be explained easily by the fact that individuals who read homophile magazines and who respond to advertisements asking for volunteers on homosexual research may be biased.

However, it is important to note that studies based on random samples of the population (not selected using homophile publications) also show a significant familial link for sexual orientation. However, even in these studies, Kendler et al. (2000) note "sexual orientation was substantially influenced by genetic factors, but family environment may also play a role" (p. 1846).

The measurement of sexual orientation has also been problematic within the study of sexual orientation. Sexual orientation can be measured during a number of different scales. In some cases, homosexuality can be defined simply through subjects answering yes to questions that indicate sexual thoughts about homosexuality. In other cases, homosexuality is defined through self-identification or life experiences. Importantly, rates of familial homosexuality can differ depending on the type of criteria used to define homosexuality (Bailey and Benishay, 1993).

Part of the difficulty in defining sexual orientation comes from developing an understanding of the distribution of sexuality. The use of homosexual and bisexual people be used as one group to be contrasted with heterosexuals indicates that researchers think of sexuality can be an easily defined. In contrast, many anecdotal reports suggest that sexual orientation occurs along a wide spectrum, and thus it is often difficult to define homosexuality or heterosexuality at a specific point on the continuum. Further, homosexuality in men and women may be a different trait, and that the genetic influences on homosexuality in men will be different from that in women (Bailey et al., 1993).

Future lines of research point to attempting to determine different regions of DNA that may be linked to sexual orientation. In addition, the location of specific genes within the Xq28 region may be useful. Further, given the recent failure of Rice et al. (1999) to replicate Hamer's identification of the Xq28 region as similar within homosexuals, research that attempts to reasons for the inconsistent findings is crucial. It is interesting to note that both Rice et al. (1999) and (Hamer et al., 1993) used homophile publications to attract subjects, and yet had different results. As such, the problem with replicating the Xq28 findings may lie in the small sample sizes used.

In summary, current research seems to indicate that sexual orientation is shaped early in life, and that genetic factors play an important role. At an early age, biological, psychological and social factors interact to shape an individual's sexual orientation. However, a great deal of work remains to determine the exact nature of both genetic and environmental factors in the determination of sexual orientation.

The study proposed here will attempt to address many of the common methodological problems that have been associated with research into the genetic basis of homosexuality in the past. These problematic methodological issues include the common use of self-selecting samples, small sample sizes, and problems with the definition of homosexuality in studies that attempt to determine the genetic basis of human sexual orientation.

Proposed Research

Hypothesis: Male homosexuality is correlated with similarities in the genetic markers from region Xq28 of the X chromosome.

The proposed study will attempt to determine the relationship between male homosexuality and the Xq28 position on the X chromosome. Specifically, this study will attempt to determine if male homosexuality is correlated with similarities in the genetic markers from region Xq28 of the X chromosome. This study will attempt to correct methodological problems that may have been problematic in earlier studies. Specifically, problems with the use of self-selecting samples, small sample sizes, and problems with the definition of homosexuality will be addressed in this study.

Materials, Methods, and Procedures

Earlier studies used relatively small sample sizes, leading to potential methodological problems. In the present study, 3,000 subjects will be contacted for inclusion. Subjects will be chosen randomly from a U.S. national sample of twin and nontwin sibling pairs, as per Kendler et al., 2000. Monozygotic, dizygotic, and non-twin sibling pairs will be assessed. Respondents to an initial questionnaire will be asked to participate in the study.

While this may lead to a type of self-selecting sample (only those who reply to the sample questionnaire will be included in the study), the problems with this form of self-selection are hoped to be less than that with samples selected through homophile publications. Given that the original sample contacted is random in nature, it is hoped that the sample that agrees to participate in the study will retain a portion of this random nature.

Given that imprecise definitions of heterosexuality and homosexuality may have played role in methodological problems with earlier studies, sexual orientation will be precisely measured. Further, homosexuality will be defined so as to clearly exclude bisexual sexual orientation. The Kinsey scale of sexual orientation will be used to assess homosexuality.

Homosexuality will be defined as a scale of 5 or 6 on the Kinsey scale, while heterosexuality will be defined as a score of 0 or 1 on the Kinsey scale. Male and female groups will be assessed separately, in order to allow for the possibility that different genetic traits govern male and female sexual orientation.

Chi square tests will be used to determine the degree of similarity on the Xp28 position between groups, as per Rice et al. (2000). Further, multipoint sib pair analysis will be carried out by the computer program ASPEX, as per Rice et al. (2000).

Expected Findings and Relevance

Given the methodological problems inherent in earlier studies of similarities in the Xq28 position among homosexuals, it is uncertain whether this study will replicate earlier findings that showed that the Xq28 region of the X chromosome was similar in male homosexuals. However, the study will provide important information whether it replicates these findings or not. If the study fails to replicate earlier findings that show the Xq28 position is implicated in sexual orientation, it may allow researchers to move their focus away from a potentially misleading area of research. A failure to replicate these findings may indicate that earlier results showing a relationship between the Xq28 region and homosexuality can be attributed to methodological issues like type 1 error.

In addition, given the known influence of genetic factors in homosexual sexual orientation, it is expected that this study may find additional genetic similarities between male or female homosexual populations. As such, data from this study may be essential in helping to define the genetic basis of sexual orientation.

If this study finds evidence of a genetic basis of sexual orientation, the findings will be a significant contribution to the field of developmental psychology. In understanding how human brains grow and develop, we can better understand our adult behaviors. As such, the social and political ramifications for finding a genetic basis for homosexuality are profound.


Bailey, J. Michael. 2003. The Man Who Would Be Queen: The Science of Gender-Bending and Transsexualism. Joseph Henry Press.

Bailey, J. M and Bell, A.P. 1993. Familiality of female and male homosexuality. Behav Genet., 23(4), 313-322. Bailey, J.M., Benishay, D.S. 1993. Familial aggregation of female sexual orientation. Am J. Psychiatry, 150(2), 272-277.

Bailey, J.M., Pillard, R.C. 1991. A genetic study of male sexual orientation. Arch Gen Psychiatry, 48(12), 1089-1096.

Bailey, J.M., Pillard, R.C., Neale, M.C. & Agyei, Y. 1993. Heritable factors influence female sexual orientation. Arch. Gen. Psychiat., 50, 217-223.

Byne, W., Tobet, S., Mattiace, L.A., Lasco, M.S., Kemether, E., Edgar, M.A., Morgello, S., Buchsbaum, M.S., and Jones, L.B. 2001. The interstitial nuclei of the human anterior hypothalamus: an investigation of variation with sex, sexual orientation, and HIV status. Horm Behav,.40, 86-92.

Blanchard, R. 2001. Fraternal birth order and the maternal immune hypothesis of male homosexuality. Hormones & Behavior, 40, 105-114.

Hamer, D. H, Hu, S., Magnuson, V.L., Hu, N. And Pattatucci, A.M. 1993. A Linkage between DNA Markers on the X chromosome and Male Sexual Orientation. Science, 261, 321- 327.

Hu, S., Pattatucci, A.M., Patterson, C., Li, L., Fulker, D.W., Cherny, S.S., Kruglyak, L. And Hamer, DH (1995). Linkage between sexual orientation and chromosome Xq28 in males but not in females. Nat. Genet. 11, 248-56.

Kendler,… [END OF PREVIEW]

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