Speaker: Ronz J. Rivera II
Candidate for Bachelor of Science
Time: 2:45 PM
Place: ACAD 116
Supervisor: Dr. Allan Hook
Title: The Heritability of Sexual Orientation in Twin Studies

Abstract: Monozygotic (MZ) and dizygotic (DZ) twins from a large community-based sample of Australian twins aged 18-52 responded to a questionnaire on sexual behavior and attitudes. This large sample was used to minimize potential ascertainment and response biases. Evidence for familial aggregation of male homosexuality has been found in previous studies. However the results obtained in these studies were possibly due to volunteer biases because of the highly selected samples used. This study and the data obtained are based on anonymous responses to a questionnaire on sexual behavior and attitudes. Structural equation modeling techniques were applied to examine the causes of individual differences in responses to several items concerning sexual orientation. In a range of psychological and behavioral measures (behaviors, attitudes and feelings), significant heritabilities were observed with approximately 42 to 60 per cent of observed variance estimated to be due to genetic influences. The statistical power of the analysis was increased by the availability of multiple measures of sexual orientation, providing stronger evidence for the existence of additive genetic influences on this phenotype. Familial aggregation was also observed in other measures (sexual behavior in the past twelve months, attitude to heterosexual sex) but it was not possible to determine whether this was due to genetic or shared environmental influences.