Saul McLeodpublished People often get confused between the terms sex and gender. Sex refers to biological differences between males and females. For example, chromosomes female XX, male XYreproductive organs ovaries, testeshormones oestrogen, testosterone.
Twin studies[ edit ] A number of twin studies have attempted to compare the relative importance of genetics and environment in the determination of sexual orientation. Self reported zygositysexual attraction, fantasy and behaviours were assessed by questionnaire and zygosity was serologically checked when in doubt.
Other researchers support biological causes for both men and women's sexual orientation. Women showed a statistically non-significant trend to weaker influence of hereditary effects, while men showed no effect of shared environmental effects.
The use of all adult twins in Sweden was designed to address the criticism of volunteer studies, in which a potential bias towards participation by gay twins may influence the results; Biometric modeling revealed that, in men, genetic effects explained.
Corresponding estimates among women were.
Several lines of research suggest that ____ during critical periods of prenatal development may influence sexual orientation as an adult. hormonal secretions Recent evidence suggests that the ____ plays a particularly central role in the modulation of emotion. sexual behavior, sexual attraction, and sexual identity among males and females aged 15–44 years in the United States, based on the – National Survey of Family Growth (NSFG). Opinions differ on the origins of an individual's sexual orientation and sexual behavior. Evolutionary perspectives on human coupling, They also deal with the influence of biological factors on other aspects of sexuality, such .
Although wide confidence intervals suggest cautious interpretation, the results are consistent with moderate, primarily genetic, familial effects, and moderate to large effects of the nonshared environment social and biological on same-sex sexual behavior.
Nonetheless, it is possible to conclude that, given the difference in sexuality in so many sets of identical twins, sexual orientation cannot be attributed solely to genetic factors. Gringas and Chen describe a number of mechanisms which can lead to differences between monozygotic twinsthe most relevant here being chorionicity and amniocity.
Monoamniotic twins share a hormonal environment, but can suffer from the 'twin to twin transfusion syndrome' in which one twin is "relatively stuffed with blood and the other exsanguinated". In Dean Hamer and colleagues published findings from a linkage analysis of a sample of 76 gay brothers and their families.
Gay brothers who showed this maternal pedigree were then tested for X chromosome linkage, using twenty-two markers on the X chromosome to test for similar alleles. This was popularly dubbed the "gay gene" in the media, causing significant controversy.
In the full sample they did not find linkage to Xq Significant linkage was also detected in the pericentromeric region of chromosome 8, overlapping with one of the regions detected in the Hamer lab's previous genomewide study. The authors concluded that "our findings, taken in context with previous work, suggest that genetic variation in each of these regions contributes to development of the important psychological trait of male sexual orientation".
Female sexual orientation does not seem to be linked to Xq28,   though it does appear moderately heritable. In a study population composed of more than participants, Ellis et al. They also found that "unusually high" proportions of homosexual males and homosexual females were Rh negative in comparison to heterosexuals.
As both blood type and Rh factor are genetically inherited traits controlled by alleles located on chromosome 9 and chromosome 1 respectively, the study indicates a potential link between genes on autosomes and homosexuality.
In the common fruit fly Drosophila melanogasterthe complete pathway of sexual differentiation of the brain and the behaviors it controls is well established in both males and females, providing a concise model of biologically controlled courtship. Without the gene, the mice exhibited masculine sexual behavior and attraction toward urine of other female mice.
Those mice who retained the gene fucose mutarotase FucM were attracted to male mice. According to Dean Hamer and Michael Bailey, genetic aspects are only one of the multiple causes of homosexuality. The research consisted of 1, homosexual men and 1, heterosexual men.
Levay's research suggested that the hypothalamus of gay men is different from straight men. The researchers found another gene, named "thyroid stimulating hormone receptor" TSHR on chromosome 14 which dna sequence is different also for gay men.
The previous research also indicated that grave disease had been seen more in gay men than in straight men. It had been presumed that the overactive TSHR hormone lowered body weight in gay people.
Epigenetic theories of homosexuality A study suggests linkage between a mother's genetic make-up and homosexuality of her sons. Women have two X chromosomes, one of which is "switched off".
The inactivation of the X chromosome occurs randomly throughout the embryo, resulting in cells that are mosaic with respect to which chromosome is active. In some cases though, it appears that this switching off can occur in a non-random fashion.
This maternal immunization hypothesis MIH begins when cells from a male fetus enter the mother's circulation during pregnancy or while giving birth. These Y-linked proteins would not be recognized in the mother's immune system because she is female, causing her to develop antibodies which would travel through the placental barrier into the fetal compartment.The first major scientist to analyze human sexual behavior in the US was Alfred Kinsey.
The highlight of their research was the physiological breakdown of the sexual act called the sexual Although researchers believe that environmental influences probably affect sexual orientation, these factors have NOT yet been identified. Definition of Terms and Concepts Related to Sex, Gender, and Sexual Orientation* It is important to recognize the difference between sexual orientation and sexual behavior as well as the differences among sexual orientation, gender identity, and gender role.
Sexual orientation is such a controversial subject that people cannot even agree about how the term sexual orientation should be defined.
Some people argue over whether it refers to sexual behavior, sexual attraction, emotional attraction, or all three. Affect fetal brain development and sexual orientation.
Sexual behavior. Biological Factors in Sexual Dysfunctions Arousal of peripheral sex organs and nervous system, spinal cord, and brain. Activity within any of these areas may impair sexual function.
Sexual Orientation - Our desire to engage in sexual behavior with someone is also influenced by sexual orientation. Sexual orientation refers to the direction of an individual's sexual . The other, the Institute for Sex Research (later renamed Kinsey Institute for Research in Sex, Gender, and Reproduction), begun in by the American sexologist Alfred Charles Kinsey at Indiana University in Bloomington, undertook the study of human sexual behaviour.