Presentation on theme: "TWO ADDITIONAL COMPONENTS OF HUMAN SEXUALITY"— Presentation transcript:
1 TWO ADDITIONAL COMPONENTS OF HUMAN SEXUALITY Gender Identification & Sexual OrientationWhat is known about their genetic regulation?Gender IdentificationAbility of children to identify with and absorb gender rolesMost male infants grow up to think of themselves as boys and then menMost female infants think of themselves as girls and then women
2 TRANSEXUALSIndividuals who have made a gender identification that is discordant with their biological sexConsider themselves as women trapped in a male body or men trapped in a female body
3 TRANSVESTITESMen who dress in women’s clothingNot considered to be a failure of gender identification but rather individuals who internalize both gender roles and express one or the other at various times in their livesHow do we assign gender to a newborn baby?
4 GENDER ASSIGNMENTAt birth a newborn’s gender is assigned on the basis of the appearance of it’s external genitalsRecorded on the birth certificate1/2,000 births are children born with ambiguous genitaliaTreatment may include sexual correction of the external genitaliaSometimes to a sex different than the chromosomal sex
5 GENDER IDENTITY2000 William Reiner of John Hopkins University followed the fates of 14 children born with pelvic field defectsThese individuals were XY with normal testicles but no penis12 were reassigned as female and all behaved as boys throughout childhood6 declared themselves male sometime between the ages of 5-12 years old
6 Levels of sexual identity TimingEventsLevelFertilizationXY=maleXX=femaleChromosomal/genetic sex9-16 weeks post fertilizationUndifferentiated structures becomes testis or ovaryGonadal sex8 weeks post fertilization to pubertyInternal and external reproductive structuresPhenotypic sexchildhoodStrong feelings of being male or female developGender identity
7 Gender is not just another train GENDER IDENTITYGender is not just another trainIt is the keystone trait, the rest of our identity develops from our genderDecisions regarding gender must be based onGonadal sexChromosomal sexPresence or absence of functional SRY locus
8 SEXUAL ORIENTATIONLook at sexual orientation as a variable phenotype in the populationMake a distinction between gender identification and sexual orientationMost gay men and lesbian women have a gender identification consistent with their biological sexBut they are physically attracted to members of the same sexThere may be some evidence that sexual orientation may have a genetic basisMust look at the heritability of a trait
9 HERITIBILITYEstimate of how much of the variation in a trait is genetic and how much is environmentalOne method of doing this is by twin studiesCompare how alike ( or concordant) identical twins are with how alike fraternal twins are for the same traitIdentical twins have the same genotype, if reared together have similar environmentFraternal twins have different genotypes but similar environment
10 SEXUAL ORIENTATION Studies done in 1991 on twins Males: In identical twins, when one twin is gay about 52% of the time the other twin is also gayIn fraternal twins when one is gay about 22% of the time the other twin is also gayIn male siblings when one is gay about 13% of the time the brother is also gay
11 SEXUAL ORIENTATION Studies done in 1991 on twins Females: In identical twins, when one twin is a lesbian about 50% of the time the other twin is also a lesbianIn fraternal twins, when one is a lesbian about 16% of the time the sister is also a lesbianIn female siblings when one is a lesbian about 13% of the time the sister is also a lesbian
12 SEXUAL ORIENTATIONDetermination of sexual orientation can not be wholly geneticIf it were concordant then identical twins would either both be homosexual or heterosexual, the way that traits like Down syndrome or cystic fibrosis or color blindness are.When a trait is wholly genetic then the concordance in twins is equal to one.With homosexuality only 1/2 of the time are both twins gay.
13 SEXUAL ORIENTATIONThere may be a genetic component because genetically identical individuals are more likely to be the same for sexual orientation that genetically different individualsSiblings of gay individuals are also gay about 13% of the timeThis is much higher than the national average incidence of gays, which is about %Is this due to genetic or environmental factors?
14 SEXUAL ORIENTATIONSibs are more genetically alike than non-related individuals in the populationThe environment they are reared in is also more similar than non-related individualsIdeal study would be to look at sibs reared apart where one sib is homosexualSuch a study would be difficult to do for obvious reasonsTwins reared apart where one or both is homosexual may not be a very large sample size
15 SEXUAL ORIENTATIONIf there is a genetic component to sexual orientation, it seems to be not fully penetrant1/2 of the time an individual with the same genetic make up will not express the phenotype of homosexualityTo do genetic studies you must first define the phenotype clearly and unambiguouslyVery difficult to do when looking at homosexuality
16 SEXUAL ORIENTATION1993 Dr. Dean Hamer and his colleges at NIH wanted to examine the genetics of male homosexualityUsed 2 methods to assess phenotypeSelf assessment, where you ask the individual of they are homosexualKinsey scale is a set of psychological tests to determine sexual orientationThe 2 methods seem to correlate in Hamer’s study
17 Dr. Hamer’s First StudyFirst group consisted of 76 self identified gay men and their relatives over the age of 18ResultsBrother of gay man had 14% chance of being gayCompared to 5-10% chance for males in general populationMaternal uncles and sons of maternal aunts had a 7-8% chance of being gayDid not see similar result for paternal uncles or sons of paternal aunts Here the chance of being gay was in the 1-5% range, the same as the general population
18 Dr. Hamer’s First StudyResults suggested an X linked determinant for sexual orientationBecause mom’s male siblings and her nephews seemed to have a higher chance of being homosexual than the general populationAnd they have the possibility of sharing an X chromosome with mom
19 Dr. Hamer’s First StudyPaternal uncles or cousins on father’s side can not share X chromosome with the male in question but maternal uncles or cousins canDad gave his homosexual son his Y chromosomeHe got his X chromosome from momHamer saw a higher frequency of concordance among relatives who could share an X chromosomeWanted to further study this maternal componentSo he did a second study
20 Dr. Hamer’s Second Study Looked at 38 families in which at least 2 sons were gay38 pairs of homosexual brothers and their relativesThis study group consisted of gay men willing to participate and involve their familiesAssessing the phenotype of volunteers is fairly straight forwardThey are all openly gay
21 Dr. Hamer’s Second Study Found maternal uncles and sons of maternal aunts had 10-13% chance of being gayCompared to 7 - 8% from the first studyIf the trait followed Mendelian inheritance would expect 50% for maternal uncle and 25% for son of maternal auntStill the results were encouraging and Dr. Hamer went on to look for the genetic component
22 Dr. Hamer’s Third StudyIn this study Dr. Hamer tried to find a possible gene on the X chromosomeThe mother of a homosexual male could be heterozygous for the geneLooked at 40 pairs of gay brothersThese brothers should share a specific region of one of the mother’s X chromosomesThe region that predisposes them to homosexuality
23 Dr. Hamer’s Third StudyBrothers were as likely to have 2 different alleles as they were to both share one of the two given maternal allelesExcept for one region near the tip of the long arm of the X chromosomeIn this region Xq 28 the two homosexual brothers shared the same allele in 33 out of the 40 casesInterpreted this to mean that this region contains genes that may predispose an individual to homosexuality
24 Dr. Hamer’s Third StudyDr. Hamer looked at 5 DNA markers in region Xq 28These sequences are highly variable in the general populationBut in his study group 33 out of the 40 pairs of gay brothers were identical in this regionNow he had a DNA sequence that was more common among homosexual brothersHe concluded that this region could predispose a male to homosexuality
26 Went on to a fourth study Dr. Hamer’s Third StudyFindings indicate a correlation between the genotype at Xq 28 and sexual orientation but it also means that there could be other genes or environmental influences at workWent on to a fourth studyLooked at heterosexual brothers of these 40 homosexual brothers and found that only 22% of them shared the allele at Xq28Most of the heterosexual brothers did not carry the allele but 22% of them did
27 CRITISISMS OF THE WORK Small sample size 40 pairs of gay brothersWork only identified DNA sequences that are more common among homosexual brothers, it did not identify a causative gene
28 IMPORTANT QUESTIONS TO CONSIDER How do the researchers define phenotype?Is it self identified?What population did they study?Are they openly gay individuals only?What was the sample size?What is the control group?Does the study look at genetic component or environmental component or genetic environmental interaction?
29 Genetically Induced Behavior The normal eye gene allows cells to break down tryptophan, which is required to make the hormone serotoninExpression of the white gene in all cells reduces the levels of serotonin in the brainIn other animals reduced levels of serotonin in the brain is also associated with homosexual behavior