Eye color, hair color, blood type, and the rhesus factor: exploring possible genetic links to sexual orientation

Redheaded women are more sexually active than other women, but it is probably due to their suitors

Women with red hair color, i.e., 1–9% of female Europeans, tend to be the subject of various stereotypes about their sexually liberated behavior. The aim of the present case–control study was to explore whether a connection between red hair color and sexual behavior really exists using data from 110 women (34% redheaded) and 93 men (22% redheaded). Redheadedness in women, correlated with various traits related to sexual life, namely with higher sexual desire as measured by Revised Sociosexual Orientation Inventory, with higher sexual activity and more sexual partners of the preferred gender over the past year, earlier initiation of sexual life, and higher sexual submissiveness. Structural equation modelling, however, showed that sexual desire of redheaded women mediated neither their higher sexual activity nor their higher number of sexual partners. These results indirectly indicate that the apparently more liberated sexual behavior in redheaded women could be the consequence of potential mates’ frequent attempts to have sex with them. Our results contradicted the three other tested models, specifically the models based on the assumption of different physiology, faster life history strategy, and altered self-perception of redheaded women induced by stereotypes about them. Naturally, the present study cannot say anything about the validity of other potential models that were not subjects of testing.

Genome-Wide Association Study of Male Sexual Orientation

Family and twin studies suggest that genes play a role in male sexual orientation. We conducted a genome-wide association study (GWAS) of male sexual orientation on a primarily European ancestry sample of 1,077 homosexual men and 1,231 heterosexual men using Affymetrix single nucleotide polymorphism (SNP) arrays. We identified several SNPs with p < 10-5, including regions of multiple supporting SNPs on chromosomes 13 (minimum p = 7.5 × 10-7) and 14 (p = 4.7 × 10-7). The genes nearest to these peaks have functions plausibly relevant to the development of sexual orientation. On chromosome 13, SLITRK6 is a neurodevelopmental gene mostly expressed in the diencephalon, which contains a region previously reported as differing in size in men by sexual orientation. On chromosome 14, TSHR genetic variants in intron 1 could conceivably help explain past findings relating familial atypical thyroid function and male homosexuality. Furthermore, skewed X chromosome inactivation has been found in the thyroid condition, Graves' disease, as well as in mothers of homosexual men. On pericentromeric chromosome 8 within our previously reported linkage peak, we found support (p = 4.1 × 10-3) for a SNP association previously reported (rs77013977, p = 7.1 × 10-8), with the combined analysis yielding p = 6.7 × 10-9, i.e., a genome-wide significant association.

Digit ratio (2D:4D), ABO blood type, and the Rhesus factor

Twin and family study findings indicate a substantial heritability of digit ratio (2D:4D), a putative marker for the masculinizing effects of prenatal androgen exposure. Functional polymorphisms of the X-linked androgen receptor gene, i.e., androgen sensitivity, contribute somewhat to the expression of 2D:4D in men, but otherwise the genetics of 2D:4D is unknown. This study investigated differences in 2D:4D by self-reported ABO blood type and Rhesus factor, two easily collectible genetic traits, in two samples (combined N=1273). Effects of blood groups on 2D:4D were small and not significant in all tests in both samples; however, two consistent patterns emerged across samples. Of the ABO types, AB had the lowest right-hand 2D:4D, the highest left-hand 2D:4D, and the lowest right-minus-left difference in 2D:4D, and Rhesus factor Rh- had higher left-hand 2D:4D and lower right-minus-left difference in 2D:4D than Rh+. If replicable, this may suggest genes contributing to the expression of 2D:4D reside in the vicinity of the gene loci (chromosomal locations: 9q34.2 and 1p36.11) of these blood groups or pleiotropic effects of the blood-group genes.

Sexual orientation matters in sexual medicine

INTRODUCTION

Homosexuality is a topic that needs to be integrated into the knowledge base of the practitioner of sexual medicine.

AIM

To present to the reader a summary of the current literature on homosexuality and sexual orientation and address specifically issues that pertain to the relationship sexual orientation and sexual medicine practice.

MAIN OUTCOME MEASURES

The information is presented in a continued medical education format, with a series of evaluation questions at the end of the activity. Methods. A review of the literature is presented and organized according to the authors' judgment of the value of the information as to provide the reader with an inclusive panorama of the issues covered.

RESULTS

Current concepts, debates, and need for further research are presented.

CONCLUSIONS

The professional of sexual medicine needs to be aware of the various topics reviewed in this article as his or her involvement in the area of sexuality can create the expectation on the part of the patients of knowingness of all aspects of human sexuality. Sexual orientation is a complex area but considerable understanding has fortunately been achieved in many issues in reference to homosexuality and heterosexuality.