We used information from nearly half a million research participants who contributed DNA and answered questions about their sexual behavior to the following large-scale research projects or direct-to-consumer genetic companies:
- UK Biobank, a population-based cohort of approximately 500,000 participants.
- 23andMe, Inc., a personal genetics company founded in 2006 that, as of May 2018, had genotyped more than 4 million customers who have consented to participate in research.
- The National Longitudinal Study of Adolescent to Adult Health (Add Health) , which originated as an in-school survey of a nationally representative sample of US adolescents.
- Molecular Genetic Study of Sexual Orientation (MGSOSO), a study specifically focused on sexual orientation in males.
- The Child and Adolescent , a study targeting all twins born in Sweden since July 1, 1992. in Sweden (CATSS)
Click here for more information about these datasets.
How did we identify geneticin each participant’s DNA?
Each person’s DNA was genotyped — that is, we determined which of the four DNA bases (A, C, G, and T) was present at each of hundreds of thousands of defined locations in the human here for videos about this topic.that are common across people. Click
How did we define same-sex sexual behavior?
The questions relevant to our study were embedded in large questionnaires assessing a wide range of characteristics. Each project which we included in our analysis approached this question in slightly different ways. Again, we use 'same-sex sexual behavior' as a catchall term, given the different ways the different databases captured this outcome (READ MORE)
- UK Biobank participants were asked: Have you ever had sex with someone of the same sex? and were classified according to if they answered this question as having only opposite-sex partners or having had any same-sex partners. See the question here. Participants who reported having had no sexual partners were excluded from our analysis, as our study focused on sexual behavior rather than identity or experience.
- Participants from 23andMe filled out a ‘Sexual Orientation Survey’ that included questions about sexual identity, sexual attraction, sexual experience, and sexual fantasies.
- Participants in the Add Health study were asked about sexual experience, romantic attraction, and sexual identity.
- In the MGSOSO study, sexual orientation was based on participants’ self-reported sexual identity and sexual feelings.
- In the CATSS study, sexual orientation was based on participants’ self-reported sexual attraction and sexual experience.
We also explored other indicators of sexuality. In particular, we examined the proportion of same-sex partners among people that, at least once, had sex with someone of the same sex in order to explore whether there were differences in the genetic associations between different aspects of sexual behavior.
To identify any links between geneticand same-sex sexual behavior, we relied on a well-established approach known as a ( ). allows scientists to systematically and statistically test millions of genetic across the entire for associations with a trait — for instance, to determine whether or not having a particular DNA base (an A, for example) at a given location is associated with same-sex sexual behavior.
Using the, or , approach, we:
- Identified genetic associated with same-sex sexual behavior.
- Explored the extent to which the genetics of same-sex sexual behavior is the same for females and males.
- Looked for evidence of overlap between the sets of genetic that influence same-sex sexual behavior and those that influence the proportion of same-sex partners among people that, at least once, had sex with someone of the same sex.
- Looked for evidence of overlap between the genetic that influence same-sex sexual behavior and those that influence other personality, reproductive, and psychiatric traits.