Homosexuality, type 1: An Xq28 phenomenon

Abstract

Despite the absence of phenotypic manifestations in alternating generations characteristic of X-linked disorders, a thesis is presented that a major type of Kinsey grades 5 and 6 male homosexuality is determined by a gene in the Xq28 region. A total of 133 families in 78 kinshps of male and female homosexual probands, in addition to 116 families (including those of 40 famous homosexuals) from the literature, revealed an unbalanced secondary sex ratio in the maternal generation of male, but not of female, homosexuals. On the maternal side, in this study, the ratio of all uncles to all aunts of 90 males homosexuals was 132/209, chi 2 = 8.52, p = 0.004. On the maternal side for the total of all sources, the ratio of uncles to aunts of male homosexuals was 241/367, chi 2 = 13.20; p < 0.0001. The male/female ratio of the total number of maternal sibships bearing homosexuals (310/628: 0.491) was a measure of fetal wastage of the mothers' male sibs; 49%. This ratio was very close to that of the total number of children born to fathers affected with any one of nine Xq28-linked male semilethal conditions (255/508: ratio 0.556); for the difference between the two populations chi 2 = 0.859, p = 0.354. The male/female ratio of the total number of children born to female carriers of any one of these same conditions (1,232/1,062: ratio 1.16), chi 2 = 13.8 p < or = 0.0001, is close to that of the total number of children in homosexual sibships: 511/413, chi 2 = 10.4, p = 0.005. Between the number of children born to Xq28 mothers and to those born of mothers of homosexuals chi 2 = 0.581, p = 0.446. One may readily surmise that the maternal influence so often related to homosexuality may lie in the mother being a genetic carrier, with traits thereto associated. In this study, 65% of the mothers of homosexuals had no or only one live-born brother. Additional support for a genetic hypothesis is found in the occurrence of multiple instances--almost exclusively among maternal relatives--of infertility, spontaneous abortions, miscarriages, stillbirths, remaining single past age 30, and suicide. Of 109 male and 43 female homosexual index cases in the present series there were 6 instances of brother/sister homosexual sibships.(ABSTRACT TRUNCATED AT 400 WORDS)

Maternal inheritance, sexual conflict and the maladapted male

“…[18]), Sykes [19] has proposed that male homosexuality might stem from incomplete penetrance of a mitochondrial haplotype selected for its ability to kill males during intrauterine development. Consistent with this hypothesis is the finding that maternal aunts significantly outnumber maternal uncles in both homosexual [20] and transsexual men [21]. Such female bias is not evident in the males' paternal relatives or in the relatives of lesbians and female transsexuals.…”

Avuncular Tendencies and the Evolution of Male Androphilia in Samoan Fa’afafine

“…Camperio Ciani, Corna, and Capiluppi (2004) reported that the female maternal relatives (i.e., mothers, grandmothers, aunts) of androphilic men exhibit greater fecundity compared to the female maternal relatives of gynephilic men in an Italian sample (see also Camperio Ciani, Cermelli, & Zanzotto, 2008;Iemmola & Camperio Ciani, 2008). Other studies have reported elevated fecundity for the mothers (King et al, 2005;Rahman et al, 2008), maternal grandmothers (McKnight & Malcolm, 2000) and maternal aunts (Bailey et al, 1999;Rahman et al, 2008;Turner, 1995) of androphilic males relative to their gynephilic counterparts. VanderLaan (2007a, 2007b) reported that the mothers of fa'afafine were significantly more fecund than those of gynephilic men.…”

Extreme skewing of X chromosome inactivation in mothers of homosexual men

“…There was no difference in mean skewing between controls and mothers of gay men An increased maternal aunt/uncle ratio was found for male-to-female transsexuals (Green and Keverne 2000) and homosexual men (Turner 1995). Since this increased ratio is hypothesized to be caused by male lethality, we analyzed the sister/brother ratio in our sample of mothers with and without extreme skewing of X-inactivation.…”

“…Variation in human sexual preference has a substantial genetic component, and a maternal bias to the inheritance pattern in males was found in some (Green and Keverne 2000;Hamer et al 1993;Turner 1995) but not all (Bailey et al 1999) studies. From the earliest work on the genetic basis of sexual orientation, the X chromosome was studied as a possible location for genes influencing this trait.…”