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[[File:Chromosome X Xq28.png|thumb|The human [[X chromosome]] with Xq28 (green) located at the tip of the long arm of the chromosome. Studies of the X chromosome as well as the entire [[human genome]] have linked Xq28 to the heredity of [[homosexuality]] in human males.]]
[[File:Chromosome X Xq28.png|thumb|The human [[X chromosome]] with Xq28 (green) located at the tip of the long arm of the chromosome. Studies of the X chromosome as well as the entire [[human genome]] have linked Xq28 to the heredity of [[homosexuality]] in human males.]]
'''Xq28''' is a [[chromosome band]] and [[genetic marker]] situated at the tip of the [[X chromosome]] which has been studied since at least 1980.<ref>{{cite journal |pmid=6930669 |year=1980 |last1=Pai |first1=GS |last2=Sprenkle |first2=JA |last3=Do |first3=TT |last4=Mareni |first4=CE |last5=Migeon |first5=BR |title=Localization of loci for hypoxanthine phosphoribosyltransferase and glucose-6-phosphate dehydrogenase and biochemical evidence of nonrandom X chromosome expression from studies of a human X-autosome translocation |volume=77 |issue=5 |pages=2810–3 |pmc=349494 |journal=Proceedings of the National Academy of Sciences of the United States of America |doi=10.1073/pnas.77.5.2810|bibcode = 1980PNAS...77.2810P }}</ref> The band contains three distinct regions, totaling about 8 [[Base pair|Mbp]] of genetic information.<ref>{{cite journal |bibcode=1996PNAS...93.1298D |jstor=38791 |title=A Compositional Map of Human Chromosome Band Xq28 |author1=De Sario |first1=Albertina |last2=Geigl |first2=Eva-Maria |last3=Palmieri |first3=Giuseppe |last4=d'Urso |first4=Michele |last5=Bernardi |first5=Giorgio |volume=93 |year=1996 |pages=1298–302 |journal=Proceedings of the National Academy of Sciences of the United States of America |doi=10.1073/pnas.93.3.1298 |pmid=8577758 |issue=3 |pmc=40074}}</ref> The marker came to the public eye in [[1993 in science|1993]] when studies by [[Dean Hamer]] and others indicated a [[Biology and sexual orientation|link]] between the Xq28 marker and male [[sexual orientation]].<ref name=Science>{{cite journal |doi=10.1126/science.8332896 |title=A linkage between DNA markers on the X chromosome and male sexual orientation |year=1993 |last1=Hamer |first1=D. |last2=Hu |first2=S |last3=Magnuson |first3=V. |last4=Hu |first4=N |last5=Pattatucci |first5=A. |journal=Science |volume=261 |issue=5119 |pages=321–7 |pmid=8332896|bibcode = 1993Sci...261..321H }}</ref>
'''Xq28''' is a [[chromosome band]] and [[genetic marker]] situated at the tip of the [[X chromosome]] which has been studied since at least 1980.<ref>{{cite journal |pmid=6930669 |year=1980 |last1=Pai |first1=GS |last2=Sprenkle |first2=JA |last3=Do |first3=TT |last4=Mareni |first4=CE |last5=Migeon |first5=BR |title=Localization of loci for hypoxanthine phosphoribosyltransferase and glucose-6-phosphate dehydrogenase and biochemical evidence of nonrandom X chromosome expression from studies of a human X-autosome translocation |volume=77 |issue=5 |pages=2810–3 |pmc=349494 |journal=Proceedings of the National Academy of Sciences of the United States of America |doi=10.1073/pnas.77.5.2810|bibcode = 1980PNAS...77.2810P }}</ref> The band contains three distinct regions, totaling about 8 [[Base pair|Mbp]] of genetic information.<ref>{{cite journal |bibcode=1996PNAS...93.1298D |jstor=38791 |title=A Compositional Map of Human Chromosome Band Xq28 |author1=De Sario |first1=Albertina |last2=Geigl |first2=Eva-Maria |last3=Palmieri |first3=Giuseppe |last4=d'Urso |first4=Michele |last5=Bernardi |first5=Giorgio |volume=93 |year=1996 |pages=1298–302 |journal=Proceedings of the National Academy of Sciences of the United States of America |doi=10.1073/pnas.93.3.1298 |pmid=8577758 |issue=3 |pmc=40074}}</ref> The marker came to the public eye in [[1993 in science|1993]] when studies by [[Dean Hamer]] and others indicated a [[Biology and sexual orientation|link]] between the Xq28 marker and male [[sexual orientation]].<ref name=Science>{{cite journal |doi=10.1126/science.8332896 |title=A linkage between DNA markers on the X chromosome and male sexual orientation |year=1993 |last1=Hamer |first1=D. |last2=Hu |first2=S |last3=Magnuson |first3=V. |last4=Hu |first4=N |last5=Pattatucci |first5=A. |journal=Science |volume=261 |issue=5119 |pages=321–7 |pmid=8332896|bibcode = 1993Sci...261..321H |url=https://zenodo.org/record/1231257 |format=Submitted manuscript }}</ref>


==Initial linkage==
==Initial linkage==
The 1993 study by [[Dean Hamer|Hamer]] ''et al.'' examined 114 families of [[Homosexuality|gay]] men in the United States and found increased rates of homosexuality among maternal uncles and cousins, but not among paternal relatives. This pattern of inheritance suggested that there might be linked genes on the [[X chromosome]], since males always inherit their copy of the X chromosome from their mothers.  Polymorphisms  of [[genetic markers]] of the X chromosome were analyzed for 40 families to see if a specific marker was shared by a disproportionate amount of brothers who were both gay. The results showed that among gay brothers, the concordance rate for markers from the Xq28 region were significantly greater than expected for random Mendelian segregation, indicating that a link did exist in that small sample. It was concluded that at least one form of male homosexuality is preferentially transmitted through the maternal side and is genetically linked to the Xq28 region.<ref name=Science />
The 1993 study by [[Dean Hamer|Hamer]] ''et al.'' examined 114 families of [[Homosexuality|gay]] men in the United States and found increased rates of homosexuality among maternal uncles and cousins, but not among paternal relatives. This pattern of inheritance suggested that there might be linked genes on the [[X chromosome]], since males always inherit their copy of the X chromosome from their mothers.  Polymorphisms  of [[genetic markers]] of the X chromosome were analyzed for 40 families to see if a specific marker was shared by a disproportionate amount of brothers who were both gay. The results showed that among gay brothers, the concordance rate for markers from the Xq28 region were significantly greater than expected for random Mendelian segregation, indicating that a link did exist in that small sample. It was concluded that at least one form of male homosexuality is preferentially transmitted through the maternal side and is genetically linked to the Xq28 region.<ref name=Science />


A follow-up study, Hu ''et al.'' (1995), conducted by the Hamer lab in collaboration with two groups of statistical experts in 1995, corroborated the original results for males with homosexual brothers sharing Xq28 at significantly elevated rates.  This study also included heterosexual brothers, who showed significantly less than expected sharing of the Xq28 region, as expected for a genetic locus that in one form is associated with same-sex attraction and in another form is associated with opposite-sex attraction.  In this study no link to Xq28 was found among homosexual females, indicating a different genetic pathway as for most sex-specific phenotypes.<ref>{{cite journal |doi=10.1038/ng1195-248 |title=Linkage between sexual orientation and chromosome Xq28 in males but not in females |year=1995 |last1=Hu |first1=Stella |last2=Pattatucci |first2=Angela M. L. |last3=Patterson |first3=Chavis |last4=Li |first4=Lin |last5=Fulker |first5=David W. |last6=Cherny |first6=Stacey S. |last7=Kruglyak |first7=Leonid |last8=Hamer |first8=Dean H. |journal=Nature Genetics |volume=11 |issue=3 |pages=248–56 |pmid=7581447}}</ref>
A follow-up study, Hu ''et al.'' (1995), conducted by the Hamer lab in collaboration with two groups of statistical experts in 1995, corroborated the original results for males with homosexual brothers sharing Xq28 at significantly elevated rates.  This study also included heterosexual brothers, who showed significantly less than expected sharing of the Xq28 region, as expected for a genetic locus that in one form is associated with same-sex attraction and in another form is associated with opposite-sex attraction.  In this study no link to Xq28 was found among homosexual females, indicating a different genetic pathway as for most sex-specific phenotypes.<ref>{{cite journal |doi=10.1038/ng1195-248 |title=Linkage between sexual orientation and chromosome Xq28 in males but not in females |year=1995 |last1=Hu |first1=Stella |last2=Pattatucci |first2=Angela M. L. |last3=Patterson |first3=Chavis |last4=Li |first4=Lin |last5=Fulker |first5=David W. |last6=Cherny |first6=Stacey S. |last7=Kruglyak |first7=Leonid |last8=Hamer |first8=Dean H. |journal=Nature Genetics |volume=11 |issue=3 |pages=248–56 |pmid=7581447|url=https://zenodo.org/record/1233407 |format=Submitted manuscript }}</ref>


Hamer's findings were highlighted in scientific journals including ''[[Science (journal)|Science]]'',<ref>{{cite journal | pmid = 8332894 | volume=261 | title=Evidence for homosexuality gene. | date=Jul 1993 | journal=Science | pages=291–2 | doi=10.1126/science.8332894}}</ref> ''[[Nature (journal)|Nature]]''<ref>{{cite journal | author = King MC | date = Jul 1993 | title = Human genetics. Sexual orientation and the X | url = | journal = Nature | volume = 364 | issue = 6435| pages = 288–9 | doi = 10.1038/364288a0 | pmid = 8332183 }}</ref> and the topic of a mini-symposium in ''[[Scientific American]]''.<ref name="Scientific American Rebuttal">{{cite journal|last=Byne|first=William|title=The Biological Evidence Challenged|journal=Scientific American|date=May 1994}}</ref><ref name="Scientific American">{{cite journal|last=Hamer|first=Dean|author2=Simon LeVay |title=Evidence for a Biological Influence in Male Homosexuality|journal=Scientific American|date=May 1994}}</ref>
Hamer's findings were highlighted in scientific journals including ''[[Science (journal)|Science]]'',<ref>{{cite journal | pmid = 8332894 | volume=261 | issue=5119 | title=Evidence for homosexuality gene | date=Jul 1993 | journal=Science | pages=291–2 | doi=10.1126/science.8332894| bibcode=1993Sci...261..291P | last1=Pool | first1=R }}</ref> ''[[Nature (journal)|Nature]]''<ref>{{cite journal | author = King MC | date = Jul 1993 | title = Human genetics. Sexual orientation and the X | url = | journal = Nature | volume = 364 | issue = 6435| pages = 288–9 | doi = 10.1038/364288a0 | pmid = 8332183 | bibcode = 1993Natur.364..288K }}</ref> and the topic of a mini-symposium in ''[[Scientific American]]''.<ref name="Scientific American Rebuttal">{{cite journal|last=Byne|first=William|title=The Biological Evidence Challenged|journal=Scientific American|date=May 1994}}</ref><ref name="Scientific American">{{cite journal|last=Hamer|first=Dean|author2=Simon LeVay |title=Evidence for a Biological Influence in Male Homosexuality|journal=Scientific American|date=May 1994}}</ref>


===Controversy===
===Controversy===
In June 1994, an article in the ''[[Chicago Tribune]]'' by [[John Crewdson]] stated that an anonymous junior researcher in Hamer’s laboratory alleged that Hamer selectively presented the data in his 1993 paper in the journal ''[[Science (journal)|Science]]''. The junior researcher had assisted in the gene mapping in Hamer's 1993 study. Shortly after voicing her questions, she was summarily dismissed from her post-doctoral fellowship in Hamer’s lab; who dismissed her could not be determined. Later, she was given another position in a different lab.<ref>{{cite web | url=http://articles.chicagotribune.com/1995-06-25/news/9506250219_1_dean-hamer-office-of-research-integrity-genes | title=Study On `Gay Gene' Challenged: Author Defends Findings Against Allegations | publisher=[[Chicago Tribune]], Washington Bureau | date=25 June 1995 | accessdate=19 February 2016 | author=Crewdson, John}}</ref> Hamer stated that Crewdson's article was "seriously in error" and denied the allegations made against him.<ref name="NoMisconductScience">{{cite journal|author1=Kaiser J|title=No Misconduct in 'Gay Gene' Study|journal=Science|date=28 Feb 1997|volume=275|issue=5304|page=1251|doi=10.1126/science.275.5304.1251b|pmid=11644902|url=http://science.sciencemag.org/content/275/5304/1251.2|accessdate=22 March 2016|publisher=American Association for the Advancement of Science|issn=1095-9203}}</ref><ref name="FinnTheScientist">{{cite journal|author1=Finn R|title=Biological Determination Of Sexuality Heating Up As A Research Field|journal=The Scientist|date=8 Jan 1996|volume=10|issue=1|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=10620510|accessdate=22 March 2016|issn=0890-3670}}</ref> An official inquiry launched by the [[Office of Research Integrity]] (ORI) to investigate  the allegations of selective presentation of the data ended in December 1996. It determined that Hamer had not committed any scientific misconduct in his study.<ref name="NoMisconductScience"/>
In June 1994, an article in the ''[[Chicago Tribune]]'' by [[John Crewdson]] stated that an anonymous junior researcher in Hamer’s laboratory alleged that Hamer selectively presented the data in his 1993 paper in the journal ''[[Science (journal)|Science]]''. The junior researcher had assisted in the gene mapping in Hamer's 1993 study. Shortly after voicing her questions, she was summarily dismissed from her post-doctoral fellowship in Hamer’s lab; who dismissed her could not be determined. Later, she was given another position in a different lab.<ref>{{cite web | url=http://articles.chicagotribune.com/1995-06-25/news/9506250219_1_dean-hamer-office-of-research-integrity-genes | title=Study On 'Gay Gene' Challenged: Author Defends Findings Against Allegations | publisher=[[Chicago Tribune]], Washington Bureau | date=25 June 1995 | accessdate=19 February 2016 | author=Crewdson, John}}</ref> Hamer stated that Crewdson's article was "seriously in error" and denied the allegations made against him.<ref name="NoMisconductScience">{{cite journal|author1=Kaiser J|title=No Misconduct in 'Gay Gene' Study|journal=Science|date=28 Feb 1997|volume=275|issue=5304|page=1251|doi=10.1126/science.275.5304.1251b|pmid=11644902|url=http://science.sciencemag.org/content/275/5304/1251.2|accessdate=22 March 2016|issn=1095-9203}}</ref><ref name="FinnTheScientist">{{cite journal|author1=Finn R|title=Biological Determination Of Sexuality Heating Up As A Research Field|journal=The Scientist|date=8 Jan 1996|volume=10|issue=1|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=10620510|accessdate=22 March 2016|issn=0890-3670}}</ref> An official inquiry launched by the [[Office of Research Integrity]] (ORI) to investigate  the allegations of selective presentation of the data ended in December 1996. It determined that Hamer had not committed any scientific misconduct in his study.<ref name="NoMisconductScience"/>


==Subsequent studies==
==Subsequent studies==


Two further studies in the 1990s gave mixed results. One was an X chromosome linkage analysis of 54 pairs of gay brothers carried out by the independent research group of Sanders ''et al.'' in 1998. The results of the study were indistinguishable from the results of the study by Hu ''et al.'': both reported that the chromosomal location of maximum sharing was locus DXS1108 and both reported similar degrees of allele sharing (66% versus 67%).<ref name=Sciencemetanalysis99/> The second study by Rice ''et al.'' in [[1999 in science|1999]] studied 52 pairs of Canadian gay brothers and found no statistically significant{{refn|name=statsignifnote|group=note|The linkage analysis by Rice ''et al.'' (1999) ''did'' report that gay brothers shared approximately 46% of their alleles at the Xq28 region. However, this result was not ''statistically significant'' because to show that male sexual orientation is influenced by a gene (or genes) at Xq28 ''in a statistically significant manner'',  their linkage analysis needed to find that gay brothers share more than 50% of their alleles at the Xq28 region. In contrast, analyses by Hamer ''et al.'' (1993), Hu ''et al.'' (1995) and the 1998 study by Sanders ''et al.'' did find greater than 50% allele sharing at Xq28 in gay brothers, thus yielding statistically significant results.<ref name=Sciencemetanalysis99 />}} linkage in [[allele]]s and [[haplotype]]s. Consequently, they concluded against the possibility of any gene in the Xq28 region having a large genetic influence on male sexual orientation (though they could not rule out the possibility of a gene in this region having a small influence).<ref name="WickelgrenScience99">{{cite journal|author1=Wickelgren I|title=Discovery of ‘Gay Gene' Questioned|journal=Science|date=23 Apr 1999|volume=284|issue=5414|page=571|doi=10.1126/science.284.5414.571|pmid=10328731|url=http://science.sciencemag.org/content/284/5414/571|accessdate=23 March 2016}}</ref> Rice ''et al.'' also asserted that their results do not exclude the possibility of finding male homosexuality genes elsewhere in the [[human genome|genome]].<ref>{{cite journal|author1=Rice G|author2=Anderson C|author3=Risch N|author4=Ebers G|title=Male homosexuality: absence of linkage to microsatellite markers at Xq28|journal=Science|date=Apr 1999|volume=284|issue=5414|pages=665–7|doi=10.1126/science.284.5414.665|pmid=10213693}}</ref> Hamer criticized the study for not selecting families for their study population based on maternal transmission as selecting only families that show an excess of maternal gay relatives is necessary to detect the Xq28 linkage.<ref name="WickelgrenScience99"/> A meta-analysis of all  data available at that time (i.e., Hamer ''et al.'' (1993), Hu ''et al.'' (1995), Rice ''et al.'' (1999), and the unpublished 1998 study by Sanders ''et al.'') indicated that Xq28 has a significant but not exclusive role in male sexual orientation.<ref name=Sciencemetanalysis99>{{cite journal|url=http://www.sciencemag.org/cgi/content/full/285/5429/803a |title=Genetics and Male Sexual Orientation |publisher=Sciencemag.org |date=1999-08-06 |accessdate=2013-11-02 |doi=10.1126/science.285.5429.803a |volume=285 |journal=Science |pages=803a}}</ref>
Two further studies in the 1990s gave mixed results. One was an X chromosome linkage analysis of 54 pairs of gay brothers carried out by the independent research group of Sanders ''et al.'' in 1998. The results of the study were indistinguishable from the results of the study by Hu ''et al.'': both reported that the chromosomal location of maximum sharing was locus DXS1108 and both reported similar degrees of allele sharing (66% versus 67%).<ref name=Sciencemetanalysis99/> The second study by Rice ''et al.'' in [[1999 in science|1999]] studied 52 pairs of Canadian gay brothers and found no statistically significant{{refn|name=statsignifnote|group=note|The linkage analysis by Rice ''et al.'' (1999) ''did'' report that gay brothers shared approximately 46% of their alleles at the Xq28 region. However, this result was not ''statistically significant'' because to show that male sexual orientation is influenced by a gene (or genes) at Xq28 ''in a statistically significant manner'',  their linkage analysis needed to find that gay brothers share more than 50% of their alleles at the Xq28 region. In contrast, analyses by Hamer ''et al.'' (1993), Hu ''et al.'' (1995) and the 1998 study by Sanders ''et al.'' did find greater than 50% allele sharing at Xq28 in gay brothers, thus yielding statistically significant results.<ref name=Sciencemetanalysis99 />}} linkage in [[allele]]s and [[haplotype]]s. Consequently, they concluded against the possibility of any gene in the Xq28 region having a large genetic influence on male sexual orientation (though they could not rule out the possibility of a gene in this region having a small influence).<ref name="WickelgrenScience99">{{cite journal|author1=Wickelgren I|title=Discovery of 'Gay Gene' Questioned|journal=Science|date=23 Apr 1999|volume=284|issue=5414|page=571|doi=10.1126/science.284.5414.571|pmid=10328731|url=http://science.sciencemag.org/content/284/5414/571|accessdate=23 March 2016}}</ref> Rice ''et al.'' also asserted that their results do not exclude the possibility of finding male homosexuality genes elsewhere in the [[human genome|genome]].<ref>{{cite journal|author1=Rice G|author2=Anderson C|author3=Risch N|author4=Ebers G|title=Male homosexuality: absence of linkage to microsatellite markers at Xq28|journal=Science|date=Apr 1999|volume=284|issue=5414|pages=665–7|doi=10.1126/science.284.5414.665|pmid=10213693|bibcode=1999Sci...284..665R}}</ref> Hamer criticized the study for not selecting families for their study population based on maternal transmission as selecting only families that show an excess of maternal gay relatives is necessary to detect the Xq28 linkage.<ref name="WickelgrenScience99"/> A meta-analysis of all  data available at that time (i.e., Hamer ''et al.'' (1993), Hu ''et al.'' (1995), Rice ''et al.'' (1999), and the unpublished 1998 study by Sanders ''et al.'' indicated that Xq28 has a significant but not exclusive role in male sexual orientation.<ref name=Sciencemetanalysis99>{{cite journal|url=http://www.sciencemag.org/cgi/content/full/285/5429/803a |title=Genetics and Male Sexual Orientation |date=1999-08-06 |accessdate=2013-11-02 |doi=10.1126/science.285.5429.803a |volume=285 |issue=5429 |journal=Science |pages=803a-803|last1=Hamer |first1=D. H }}</ref>


The authors of the meta-analysis (which included three authors of the Rice ''et al.'' study, Rice, Risch and Ebers) presented several methodological reasons due to which Rice ''et al.'' (1999) may have been unable to detect statistically significant linkage between Xq28 and male sexual orientation: the families [[genotyping|genotyped]] by Rice ''et al.'' were non-representative as they had an excess of paternal instead of maternal gay relatives thus obscuring the display of any X-chromosome linkage; the [[statistical power]] of their sample was insufficient to adequately detect linkage{{refn|name=statpowernote|group=note|There was a 35% chance that Rice ''et al.'' would not detect Xq28's linkage with homosexuality simply by chance.<ref name=Sciencemetanalysis99/>}} and they lacked definite criteria for what constituted as ''homosexuality'' (the researchers depended on their own judgement and sometimes based their judgement on a single question to the subject).<ref name=Sciencemetanalysis99/> They also lacked criteria "to select appropriate families for the study of a putative X-linked locus"<ref name=Sciencemetanalysis99/> — as they did not select families based on the presence of maternal transmission of homosexuality, the Xq28 contribution to male sexual orientation may have been hidden.<ref name="WickelgrenScience99"/> In addition, the meta-analysis revealed that the family pedigree data of Rice ''et al.'' (1999), in contrast to the genotyping data, seemed to support X chromosome linkage for homosexuality.<ref name=Sciencemetanalysis99/>{{refn|name=FamPediData|group=note|Rice ''et al.'' did not include the family pedigree data in their April 1999 report, which described only the genotyping results for a subset of 48 families. The realization that the family pedigree data actually supported X chromosome linkage came later when the data was analysed during the meta-analysis published in August 1999.<ref name=Sciencemetanalysis99/>}}
The authors of the meta-analysis (which included three authors of the Rice ''et al.'' study, Rice, Risch and Ebers) presented several methodological reasons due to which Rice ''et al.'' (1999) may have been unable to detect statistically significant linkage between Xq28 and male sexual orientation: the families [[genotyping|genotyped]] by Rice ''et al.'' were non-representative as they had an excess of paternal instead of maternal gay relatives thus obscuring the display of any X-chromosome linkage; the [[statistical power]] of their sample was insufficient to adequately detect linkage{{refn|name=statpowernote|group=note|There was a 35% chance that Rice ''et al.'' would not detect Xq28's linkage with homosexuality simply by chance.<ref name=Sciencemetanalysis99/>}} and they lacked definite criteria for what constituted as ''homosexuality'' (the researchers depended on their own judgement and sometimes based their judgement on a single question to the subject).<ref name=Sciencemetanalysis99/> They also lacked criteria "to select appropriate families for the study of a putative X-linked locus"<ref name=Sciencemetanalysis99/> — as they did not select families based on the presence of maternal transmission of homosexuality, the Xq28 contribution to male sexual orientation may have been hidden.<ref name="WickelgrenScience99"/> In addition, the meta-analysis revealed that the family pedigree data of Rice ''et al.'' (1999), in contrast to the genotyping data, seemed to support X chromosome linkage for homosexuality.<ref name=Sciencemetanalysis99/>{{refn|name=FamPediData|group=note|Rice ''et al.'' did not include the family pedigree data in their April 1999 report, which described only the genotyping results for a subset of 48 families. The realization that the family pedigree data actually supported X chromosome linkage came later when the data was analysed during the meta-analysis published in August 1999.<ref name=Sciencemetanalysis99/>}}


In 2012, a large, comprehensive [[Genome-wide association study|genome-wide linkage study]] of male sexual orientation was conducted by several independent groups of researchers.<ref name=camb20141117>{{cite journal |author=Sanders, A. R. and Martin, E. R. and Beecham, G. W. and Guo, S. and Dawood, K. and Rieger, G. and Badner, J. A. and Gershon, E. S. and Krishnappa, R. S. and Kolundzija, A. B. and Duan, J. and Gejman, P. V. and Bailey, J. M. |date=November 2014 |title=Genome-wide scan demonstrates significant linkage for male sexual orientation |url=http://journals.cambridge.org/article_S0033291714002451 |journal=Psychological Medicine |volume=45 |pages=1379–88 |doi=10.1017/S0033291714002451 |pmid=25399360}}</ref> The study population included 409 independent pairs of gay brothers from 384 families, who were analyzed with over 300,000 [[single-nucleotide polymorphism]] markers. The study confirmed the Xq28 linkage to homosexuality by two-point and multipoint (MERLIN) LOD score mapping. Significant linkage was also detected in the region near the [[centromere]] of [[chromosome 8]], overlapping with one of the regions detected in a previous genomewide linkage study by the Hamer lab. The authors concluded that "our findings, taken in context with previous work, suggest that genetic variation in each of these regions contributes to development of the important psychological trait of male sexual orientation." It was the largest study of the genetic basis of homosexuality to date and was published online in November 2014.<ref>Bob Grant for The Scientist. November 19, 2014 [http://www.the-scientist.com/?articles.view/articleNo/41472/title/Zeroing-in-on-the--Gay-Gene-/ Zeroing in on the “Gay Gene” The largest study yet of the genetic roots of homosexuality links sexual preference in men to two regions of the genome]</ref>
In 2012, a large, comprehensive [[Genome-wide association study|genome-wide linkage study]] of male sexual orientation was conducted by several independent groups of researchers.<ref name=camb20141117>{{cite journal |vauthors = Sanders AR, Martin ER, Beecham GW, Guo S, Dawood K, Rieger G, Badner JA, Gershon ES, Krishnappa RS, Kolundzija AB, Duan J, Gejman PV, Bailey JM |date = November 2014 |title = Genome-wide scan demonstrates significant linkage for male sexual orientation |url=http://journals.cambridge.org/article_S0033291714002451 |journal=Psychological Medicine |volume = 45 |issue = 7 |pages = 1379–88 |doi = 10.1017/S0033291714002451 |pmid = 25399360}}</ref> The study population included 409 independent pairs of gay brothers from 384 families, who were analyzed with over 300,000 [[single-nucleotide polymorphism]] markers. The study confirmed the Xq28 linkage to homosexuality by two-point and multipoint (MERLIN) LOD score mapping. Significant linkage was also detected in the region near the [[centromere]] of [[chromosome 8]], overlapping with one of the regions detected in a previous genomewide linkage study by the Hamer lab. The authors concluded that "our findings, taken in context with previous work, suggest that genetic variation in each of these regions contributes to development of the important psychological trait of male sexual orientation." It was the largest study of the genetic basis of homosexuality to date and was published online in November 2014.<ref>Bob Grant for The Scientist. November 19, 2014 [http://www.the-scientist.com/?articles.view/articleNo/41472/title/Zeroing-in-on-the--Gay-Gene-/ Zeroing in on the “Gay Gene” The largest study yet of the genetic roots of homosexuality links sexual preference in men to two regions of the genome]</ref>


==Other contents==
==Other contents==
Xq28 is a large, complex, and gene dense region.<ref>{{cite journal|author1=Ngun TC|author2=Vilain E|title=The Biological Basis of Human Sexual Orientation: Is There a Role for Epigenetics?|journal=Advances in Genetics|date=2014|volume=86|pages=167–84|doi=10.1016/B978-0-12-800222-3.00008-5|issn= 0065-2660|pmid=25172350|url=http://gaystudies.genetics.ucla.edu/UCLA%20Twin%20Sexual%20Orientation%20Study/Read%20More_files/Ngun.pdf|accessdate=25 March 2016}}</ref> Among its various genes are the 12 genes of the [[melanoma-associated antigen]] (MAGE) family,<ref>{{cite journal |pmid=8575766 |year=1995 |last1=Rogner |first1=UC |last2=Wilke |first2=K |last3=Steck |first3=E |last4=Korn |first4=B |last5=Poustka |first5=A |title=The melanoma antigen gene (MAGE) family is clustered in the chromosomal band Xq28 |volume=29 |issue=3 |pages=725–31 |doi=10.1006/geno.1995.9945 |journal=Genomics}}</ref> of which [[MAGEA11]] has been identified as a coregulator for the [[androgen receptor]].<ref>{{cite journal |pmid=21789088 |year=2010 |last1=Wilson |first1=EM |title=Androgen receptor molecular biology and potential targets in prostate cancer |volume=2 |issue=3 |pages=105–17 |doi=10.1177/1756287210372380 |pmc=3126091 |journal=Therapeutic advances in urology}}</ref> Mutations involving the production of [[gene duplication|extra copies]] of the [[MECP2]] and [[IRAK1]] genes within Xq28 have been associated with phenotypes including anxiety and autism in [[mouse|mice]].<ref>{{cite journal |pmid=22231481 |year=2012 |last1=Samaco |first1=RC |last2=Mandel-Brehm |first2=C |last3=McGraw |first3=CM |last4=Shaw |first4=CA |last5=McGill |first5=BE |last6=Zoghbi |first6=HY |title=Crh and Oprm1 mediate anxiety-related behavior and social approach in a mouse model of MECP2 duplication syndrome |pmc=3267865|doi=10.1038/ng.1066 |journal=Nature Genetics |volume=44 |issue=2 |pages=206–11}}</ref>
Xq28 is a large, complex, and gene dense region.<ref>{{Cite book|author1=Ngun TC|author2=Vilain E|title=The Biological Basis of Human Sexual Orientation: Is There a Role for Epigenetics?|journal=Advances in Genetics|date=2014|volume=86|pages=167–84|doi=10.1016/B978-0-12-800222-3.00008-5|issn= 0065-2660|pmid=25172350|url=http://gaystudies.genetics.ucla.edu/UCLA%20Twin%20Sexual%20Orientation%20Study/Read%20More_files/Ngun.pdf|accessdate=25 March 2016|isbn=9780128002223}}</ref> Among its various genes are the 12 genes of the [[melanoma-associated antigen]] (MAGE) family,<ref>{{cite journal |pmid=8575766 |year=1995 |last1=Rogner |first1=UC |last2=Wilke |first2=K |last3=Steck |first3=E |last4=Korn |first4=B |last5=Poustka |first5=A |title=The melanoma antigen gene (MAGE) family is clustered in the chromosomal band Xq28 |volume=29 |issue=3 |pages=725–31 |doi=10.1006/geno.1995.9945 |journal=Genomics}}</ref> of which [[MAGEA11]] has been identified as a coregulator for the [[androgen receptor]].<ref>{{cite journal |pmid=21789088 |year=2010 |last1=Wilson |first1=EM |title=Androgen receptor molecular biology and potential targets in prostate cancer |volume=2 |issue=3 |pages=105–17 |doi=10.1177/1756287210372380 |pmc=3126091 |journal=Therapeutic Advances in Urology}}</ref> Mutations involving the production of [[gene duplication|extra copies]] of the [[MECP2]] and [[IRAK1]] genes within Xq28 have been associated with phenotypes including anxiety and autism in [[mouse|mice]].<ref>{{cite journal |pmid=22231481 |year=2012 |last1=Samaco |first1=RC |last2=Mandel-Brehm |first2=C |last3=McGraw |first3=CM |last4=Shaw |first4=CA |last5=McGill |first5=BE |last6=Zoghbi |first6=HY |title=Crh and Oprm1 mediate anxiety-related behavior and social approach in a mouse model of MECP2 duplication syndrome |pmc=3267865|doi=10.1038/ng.1066 |journal=Nature Genetics |volume=44 |issue=2 |pages=206–11}}</ref>


==See also==
==See also==
* [[Biology and sexual orientation]]
* [[Biology and sexual orientation]]
* [[Daily Mail#Gay gene controversy]]
* [[Daily Mail#Gay gene controversy]]
* ''[[The Science of Desire]]''


==Notes==
==Notes==

Revision as of 22:27, 5 September 2018

File:Chromosome X Xq28.png
The human X chromosome with Xq28 (green) located at the tip of the long arm of the chromosome. Studies of the X chromosome as well as the entire human genome have linked Xq28 to the heredity of homosexuality in human males.

Xq28 is a chromosome band and genetic marker situated at the tip of the X chromosome which has been studied since at least 1980.[1] The band contains three distinct regions, totaling about 8 Mbp of genetic information.[2] The marker came to the public eye in 1993 when studies by Dean Hamer and others indicated a link between the Xq28 marker and male sexual orientation.[3]

Initial linkage

The 1993 study by Hamer et al. examined 114 families of gay men in the United States and found increased rates of homosexuality among maternal uncles and cousins, but not among paternal relatives. This pattern of inheritance suggested that there might be linked genes on the X chromosome, since males always inherit their copy of the X chromosome from their mothers. Polymorphisms of genetic markers of the X chromosome were analyzed for 40 families to see if a specific marker was shared by a disproportionate amount of brothers who were both gay. The results showed that among gay brothers, the concordance rate for markers from the Xq28 region were significantly greater than expected for random Mendelian segregation, indicating that a link did exist in that small sample. It was concluded that at least one form of male homosexuality is preferentially transmitted through the maternal side and is genetically linked to the Xq28 region.[3]

A follow-up study, Hu et al. (1995), conducted by the Hamer lab in collaboration with two groups of statistical experts in 1995, corroborated the original results for males with homosexual brothers sharing Xq28 at significantly elevated rates. This study also included heterosexual brothers, who showed significantly less than expected sharing of the Xq28 region, as expected for a genetic locus that in one form is associated with same-sex attraction and in another form is associated with opposite-sex attraction. In this study no link to Xq28 was found among homosexual females, indicating a different genetic pathway as for most sex-specific phenotypes.[4]

Hamer's findings were highlighted in scientific journals including Science,[5] Nature[6] and the topic of a mini-symposium in Scientific American.[7][8]

Controversy

In June 1994, an article in the Chicago Tribune by John Crewdson stated that an anonymous junior researcher in Hamer’s laboratory alleged that Hamer selectively presented the data in his 1993 paper in the journal Science. The junior researcher had assisted in the gene mapping in Hamer's 1993 study. Shortly after voicing her questions, she was summarily dismissed from her post-doctoral fellowship in Hamer’s lab; who dismissed her could not be determined. Later, she was given another position in a different lab.[9] Hamer stated that Crewdson's article was "seriously in error" and denied the allegations made against him.[10][11] An official inquiry launched by the Office of Research Integrity (ORI) to investigate the allegations of selective presentation of the data ended in December 1996. It determined that Hamer had not committed any scientific misconduct in his study.[10]

Subsequent studies

Two further studies in the 1990s gave mixed results. One was an X chromosome linkage analysis of 54 pairs of gay brothers carried out by the independent research group of Sanders et al. in 1998. The results of the study were indistinguishable from the results of the study by Hu et al.: both reported that the chromosomal location of maximum sharing was locus DXS1108 and both reported similar degrees of allele sharing (66% versus 67%).[12] The second study by Rice et al. in 1999 studied 52 pairs of Canadian gay brothers and found no statistically significant[note 1] linkage in alleles and haplotypes. Consequently, they concluded against the possibility of any gene in the Xq28 region having a large genetic influence on male sexual orientation (though they could not rule out the possibility of a gene in this region having a small influence).[13] Rice et al. also asserted that their results do not exclude the possibility of finding male homosexuality genes elsewhere in the genome.[14] Hamer criticized the study for not selecting families for their study population based on maternal transmission as selecting only families that show an excess of maternal gay relatives is necessary to detect the Xq28 linkage.[13] A meta-analysis of all data available at that time (i.e., Hamer et al. (1993), Hu et al. (1995), Rice et al. (1999), and the unpublished 1998 study by Sanders et al. indicated that Xq28 has a significant but not exclusive role in male sexual orientation.[12]

The authors of the meta-analysis (which included three authors of the Rice et al. study, Rice, Risch and Ebers) presented several methodological reasons due to which Rice et al. (1999) may have been unable to detect statistically significant linkage between Xq28 and male sexual orientation: the families genotyped by Rice et al. were non-representative as they had an excess of paternal instead of maternal gay relatives thus obscuring the display of any X-chromosome linkage; the statistical power of their sample was insufficient to adequately detect linkage[note 2] and they lacked definite criteria for what constituted as homosexuality (the researchers depended on their own judgement and sometimes based their judgement on a single question to the subject).[12] They also lacked criteria "to select appropriate families for the study of a putative X-linked locus"[12] — as they did not select families based on the presence of maternal transmission of homosexuality, the Xq28 contribution to male sexual orientation may have been hidden.[13] In addition, the meta-analysis revealed that the family pedigree data of Rice et al. (1999), in contrast to the genotyping data, seemed to support X chromosome linkage for homosexuality.[12][note 3]

In 2012, a large, comprehensive genome-wide linkage study of male sexual orientation was conducted by several independent groups of researchers.[15] The study population included 409 independent pairs of gay brothers from 384 families, who were analyzed with over 300,000 single-nucleotide polymorphism markers. The study confirmed the Xq28 linkage to homosexuality by two-point and multipoint (MERLIN) LOD score mapping. Significant linkage was also detected in the region near the centromere of chromosome 8, overlapping with one of the regions detected in a previous genomewide linkage study by the Hamer lab. The authors concluded that "our findings, taken in context with previous work, suggest that genetic variation in each of these regions contributes to development of the important psychological trait of male sexual orientation." It was the largest study of the genetic basis of homosexuality to date and was published online in November 2014.[16]

Other contents

Xq28 is a large, complex, and gene dense region.[17] Among its various genes are the 12 genes of the melanoma-associated antigen (MAGE) family,[18] of which MAGEA11 has been identified as a coregulator for the androgen receptor.[19] Mutations involving the production of extra copies of the MECP2 and IRAK1 genes within Xq28 have been associated with phenotypes including anxiety and autism in mice.[20]

See also

Notes

  1. ↑ The linkage analysis by Rice et al. (1999) did report that gay brothers shared approximately 46% of their alleles at the Xq28 region. However, this result was not statistically significant because to show that male sexual orientation is influenced by a gene (or genes) at Xq28 in a statistically significant manner, their linkage analysis needed to find that gay brothers share more than 50% of their alleles at the Xq28 region. In contrast, analyses by Hamer et al. (1993), Hu et al. (1995) and the 1998 study by Sanders et al. did find greater than 50% allele sharing at Xq28 in gay brothers, thus yielding statistically significant results.[12]
  2. ↑ There was a 35% chance that Rice et al. would not detect Xq28's linkage with homosexuality simply by chance.[12]
  3. ↑ Rice et al. did not include the family pedigree data in their April 1999 report, which described only the genotyping results for a subset of 48 families. The realization that the family pedigree data actually supported X chromosome linkage came later when the data was analysed during the meta-analysis published in August 1999.[12]

References

  1. ↑ Pai, GS; Sprenkle, JA; Do, TT; Mareni, CE; Migeon, BR (1980). "Localization of loci for hypoxanthine phosphoribosyltransferase and glucose-6-phosphate dehydrogenase and biochemical evidence of nonrandom X chromosome expression from studies of a human X-autosome translocation". Proceedings of the National Academy of Sciences of the United States of America. 77 (5): 2810–3. Bibcode:1980PNAS...77.2810P. doi:10.1073/pnas.77.5.2810. PMC 349494. PMID 6930669.
  2. ↑ De Sario, Albertina; Geigl, Eva-Maria; Palmieri, Giuseppe; d'Urso, Michele; Bernardi, Giorgio (1996). "A Compositional Map of Human Chromosome Band Xq28". Proceedings of the National Academy of Sciences of the United States of America. 93 (3): 1298–302. Bibcode:1996PNAS...93.1298D. doi:10.1073/pnas.93.3.1298. JSTOR 38791. PMC 40074. PMID 8577758.
  3. ↑ 3.0 3.1 Hamer, D.; Hu, S; Magnuson, V.; Hu, N; Pattatucci, A. (1993). "A linkage between DNA markers on the X chromosome and male sexual orientation" (Submitted manuscript). Science. 261 (5119): 321–7. Bibcode:1993Sci...261..321H. doi:10.1126/science.8332896. PMID 8332896.
  4. ↑ Hu, Stella; Pattatucci, Angela M. L.; Patterson, Chavis; Li, Lin; Fulker, David W.; Cherny, Stacey S.; Kruglyak, Leonid; Hamer, Dean H. (1995). "Linkage between sexual orientation and chromosome Xq28 in males but not in females" (Submitted manuscript). Nature Genetics. 11 (3): 248–56. doi:10.1038/ng1195-248. PMID 7581447.
  5. ↑ Pool, R (Jul 1993). "Evidence for homosexuality gene". Science. 261 (5119): 291–2. Bibcode:1993Sci...261..291P. doi:10.1126/science.8332894. PMID 8332894.
  6. ↑ King MC (Jul 1993). "Human genetics. Sexual orientation and the X". Nature. 364 (6435): 288–9. Bibcode:1993Natur.364..288K. doi:10.1038/364288a0. PMID 8332183.
  7. ↑ Byne, William (May 1994). "The Biological Evidence Challenged". Scientific American.
  8. ↑ Hamer, Dean; Simon LeVay (May 1994). "Evidence for a Biological Influence in Male Homosexuality". Scientific American.
  9. ↑ Crewdson, John (25 June 1995). "Study On 'Gay Gene' Challenged: Author Defends Findings Against Allegations". Chicago Tribune, Washington Bureau. Retrieved 19 February 2016.
  10. ↑ 10.0 10.1 Kaiser J (28 Feb 1997). "No Misconduct in 'Gay Gene' Study". Science. 275 (5304): 1251. doi:10.1126/science.275.5304.1251b. ISSN 1095-9203. PMID 11644902. Retrieved 22 March 2016.
  11. ↑ Finn R (8 Jan 1996). "Biological Determination Of Sexuality Heating Up As A Research Field". The Scientist. 10 (1). ISSN 0890-3670. Retrieved 22 March 2016.
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 Hamer, D. H (1999-08-06). "Genetics and Male Sexual Orientation". Science. 285 (5429): 803a-803. doi:10.1126/science.285.5429.803a. Retrieved 2013-11-02.
  13. ↑ 13.0 13.1 13.2 Wickelgren I (23 Apr 1999). "Discovery of 'Gay Gene' Questioned". Science. 284 (5414): 571. doi:10.1126/science.284.5414.571. PMID 10328731. Retrieved 23 March 2016.
  14. ↑ Rice G; Anderson C; Risch N; Ebers G (Apr 1999). "Male homosexuality: absence of linkage to microsatellite markers at Xq28". Science. 284 (5414): 665–7. Bibcode:1999Sci...284..665R. doi:10.1126/science.284.5414.665. PMID 10213693.
  15. ↑ Sanders AR, Martin ER, Beecham GW, Guo S, Dawood K, Rieger G, Badner JA, Gershon ES, Krishnappa RS, Kolundzija AB, Duan J, Gejman PV, Bailey JM (November 2014). "Genome-wide scan demonstrates significant linkage for male sexual orientation". Psychological Medicine. 45 (7): 1379–88. doi:10.1017/S0033291714002451. PMID 25399360.
  16. ↑ Bob Grant for The Scientist. November 19, 2014 Zeroing in on the “Gay Gene” The largest study yet of the genetic roots of homosexuality links sexual preference in men to two regions of the genome
  17. ↑ Ngun TC; Vilain E (2014). The Biological Basis of Human Sexual Orientation: Is There a Role for Epigenetics? (PDF). Advances in Genetics. 86. pp. 167–84. doi:10.1016/B978-0-12-800222-3.00008-5. ISBN 9780128002223. ISSN 0065-2660. PMID 25172350. Retrieved 25 March 2016.
  18. ↑ Rogner, UC; Wilke, K; Steck, E; Korn, B; Poustka, A (1995). "The melanoma antigen gene (MAGE) family is clustered in the chromosomal band Xq28". Genomics. 29 (3): 725–31. doi:10.1006/geno.1995.9945. PMID 8575766.
  19. ↑ Wilson, EM (2010). "Androgen receptor molecular biology and potential targets in prostate cancer". Therapeutic Advances in Urology. 2 (3): 105–17. doi:10.1177/1756287210372380. PMC 3126091. PMID 21789088.
  20. ↑ Samaco, RC; Mandel-Brehm, C; McGraw, CM; Shaw, CA; McGill, BE; Zoghbi, HY (2012). "Crh and Oprm1 mediate anxiety-related behavior and social approach in a mouse model of MECP2 duplication syndrome". Nature Genetics. 44 (2): 206–11. doi:10.1038/ng.1066. PMC 3267865. PMID 22231481.

External links

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