1. Studies of biological contributions to homosexuality face difficulties due to ethical and practical limitations of research on humans as well as differences between humans and animal models. 2. Genetic research has used linkage analysis and association studies to search for genes related to homosexuality, but results so far only suggest regions rather than specific genes due to complexity of multiple genetic and environmental factors. 3. Epigenetics offers a framework to study gene-environment interactions through examining methylation differences between identical twins who differ in sexual orientation, but causes of those methylation differences remain unknown.

1. Section 10
3/13/13

2. Today
• Quiz 3 review
• Course evaluations
• Vilain lecture material from week 9
• Saguy – review of sociology readings

3. Difficulties in studying biological
contribution to homosexuality
• Some studies on humans are neither practical nor
ethical
• Animal models may not be optimal because of
human/animal differences
• Recruitment difficulties
– Selection bias
– How is homosexuality defined?
– What is the object of study? Tissue? Genes? An area
of the brain? During what period of development?
• Gene environment interactions

4. Looking for “a” gene
• Linkage analysis: don’t know which specific genes are
responsible
– Narrowing it down: whichever parts of the genome are
shared between affected family members
– Need 2+ affected family members
• Identify family members with the same trait.
Find the genetic marker for that trait
• Repeat the process multiple times to identify a
genetic marker that is statistically more linked
to a particular trait
• In other words, search for a genetic region that
is passed on to affected members in a family
more than to those not affected

5. Linkage analyses
• Suggests Xq28
– This region is on the tip of the X chromosome
• However, linkage studies suggest other
autosomal regions (not on sex chromosomes)
• Could be more than one gene and multiple
physiological determinants/factors
• 12 million base pairs in human DNA makes the
search challenging

6. Looking for “a” gene
• Association study: similar to linkage, but in larger
populations. (Xq28 region = many alleles)
– E.g.: Are gay people much more (or less) likely to have a
specific allele than straight people?
• Search for a genetic marker that is shared
amongst people with a common trait. Requires
(1) a large group of individuals with the trait
and (2) a comparison to a large group of closely
matched controls
• Families not required

7. Looking for “a” gene
• Candidate genes
• Best guess for a gene is nominated and then
studied

8. Looking for “a” gene
• Gene expression
• Examine
microarrays, comparing
heterosexual and homosexual
individuals (sheep in this case)
• Do some genes show signs of
stronger expression in the
phenotype?
• Gene expression in brain
regions compared – null
results

9. Epigenetics
• Gene expression varies and can be regulated
by methylation
• Methylation acts on cytosine
• Epigenome seen as interface between
environmental signals and persistent behavior
• But it is currently impossible to determine
“how much” environmental influence

10. Epigenetics continued
• Can be viewed as “a unifying solution for
gene-environment interactions”
• Only have to look for methylation – not the
cause of methylation
• In addition, it can also be assumed that there
will not be a one-to-one correlation between
the presence of a particular allele combination
and homosexuality
• Therefore, twin studies may be useful

11. Twin studies
• Because while MZ twins share 100% of their
DNA, they do not have the same epigenetic
patterns
• Recall concordance rates for male
homosexuals:
– MZ = 52%
– DZ = 22%

12. Twin studies
• Looking at some of the regions of the genome
identified by linkage analysis
• Looked for differences between the
methylation of these genes between twins
• 4-5% differences in methylation

13. The ex-gay movement
•1. History of Mental Health Attitudes toward
Homosexuality
•2. Sexual Conversion Therapies in a Cultural
Context
•3. Clinical/Research Issues

14. History Of Mental Attitudes
•19th: From Sin to Sick
• - from judgment to “science”: ex. Degeneracy theory  “arrested
development” (Freud)
•Mid 20th: DSM : efforts to standardize mental health in general
• -1952: Sociopathic Personality Disturbance
• -1953: Evelyn Hooker – major evidence to the contrary
• -1973: APA Decision to remove homosexuality
• Interaction with culture/politics: i.e. activism informed the APA
• not a mental illness  “normalization”  cultural war

15. “Conversion”/”Reparative”
Therapy in Context
- Normalization Provokes Culture wars
-Opposing Views on Homosexuality:
-Normal/Identity Model: accepting one's normal
homosexual orientation
-Illness/Behavior Model: rejection of identity model
and says it is abnormal

16. Clinical and Research Issues
•- Robert L. Spitzer: Reparative Therapy Works [?]
– Scales of sexual orientation:
•attraction, identity, sexual behavior
• Critiques:
–no follow-up or face to face interviews
–retrospective accounts
–recruitment and sample bias
–NO peer review

17. Gay Rights, Research, and Politics
• Research about the origins or sexual orientation
is tied up in politics.
– Anti-gay activists use “reparative” therapy
as evidence that sexual orientation is
“changeable” and a “choice” and thus not
deserving of legal rights and protections.
– This stance is used to justify legal
discrimination in employment, marriage
rights, and other areas.

18. Saguy exercise
• Race Covering Flaunting
• Sex Appearance
• Motherhood
• Class Affiliation
• Fat
Activism
• Others
Association