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Homosexual behavior due to genetics and environmental factors
June 30, 2008Homosexual behaviour is largely shaped by genetics and random environmental factors, according to findings from the world's largest study of twins.
Writing in the scientific journal Archives of Sexual Behavior, researchers from Queen Mary's School of Biological and Chemical Sciences, and Karolinska Institutet in Stockholm report that genetics and environmental factors (which are specific to an individual, and may include biological processes such as different hormone exposure in the womb), are important determinants of homosexual behaviour.
Dr Qazi Rahman, study co-author and a leading scientist on human sexual orientation, explains: "This study puts cold water on any concerns that we are looking for a single 'gay gene' or a single environmental variable which could be used to 'select out' homosexuality - the factors which influence sexual orientation are complex. And we are not simply talking about homosexuality here - heterosexual behaviour is also influenced by a mixture of genetic and environmental factors.
The team led by Dr Niklas Långström at Karolinska Institutet conducted the first truly population-based survey of all adult (20-47 years old) twins in Sweden. Studies of identical twins and non-identical, or fraternal, twins are often used to untangle the genetic and environmental factors responsible for a trait. While identical twins share all of their genes and their entire environment, fraternal twins share only half of their genes and their entire environment. Therefore, greater similarity in a trait between identical twins compared to fraternal twins shows that genetic factors are partly responsible for the trait.
This study looked at 3,826 same-gender twin pairs (7,652 individuals), who were asked about the total numbers of opposite sex and same sex partners they had ever had. The findings showed that 35 per cent of the differences between men in same-sex behaviour (that is, that some men have no same sex partners, and some have one or more) is accounted for by genetics. Rahman explains:
"Overall, genetics accounted for around 35 per cent of the differences between men in homosexual behaviour and other individual-specific environmental factors (that is, not societal attitudes, family or parenting which are shared by twins) accounted for around 64 per cent. In other words, men become gay or straight because of different developmental pathways, not just one pathway."
For women, genetics explained roughly 18 per cent of the variation in same-sex behaviour, non-shared environment roughly 64 per cent and shared factors, or the family environment, explained 16 per cent.
The study shows that genetic influences are important but modest, and that non-shared environmental factors, which may include factors operating during foetal development, dominate. Importantly, heredity had roughly the same influence as shared environmental factors in women, whereas the latter had no impact on sexual behaviour in men.
Dr Rahman adds: "The study is not without its limitations - we used a behavioural measure of sexual orientation which might be ok to use for men (men's psychological orientation, sexual behaviour, and sexual responses are highly related) but less so for women (who show a clearer separation between these elements of sexuality). Despite this, our study provides the most unbiased estimates presented so far of genetic and non-genetic contributions to sexual orientation."
Queen Mary, University of London
The team led by Dr Niklas Långström at Karolinska Institutet conducted the first truly population-based survey of all adult (20-47 years old) twins in Sweden. Studies of identical twins and non-identical, or fraternal, twins are often used to untangle the genetic and environmental factors responsible for a trait. While identical twins share all of their genes and their entire environment, fraternal twins share only half of their genes and their entire environment. Therefore, greater similarity in a trait between identical twins compared to fraternal twins shows that genetic factors are partly responsible for the trait.
This study looked at 3,826 same-gender twin pairs (7,652 individuals), who were asked about the total numbers of opposite sex and same sex partners they had ever had. The findings showed that 35 per cent of the differences between men in same-sex behaviour (that is, that some men have no same sex partners, and some have one or more) is accounted for by genetics. Rahman explains:
"Overall, genetics accounted for around 35 per cent of the differences between men in homosexual behaviour and other individual-specific environmental factors (that is, not societal attitudes, family or parenting which are shared by twins) accounted for around 64 per cent. In other words, men become gay or straight because of different developmental pathways, not just one pathway."
For women, genetics explained roughly 18 per cent of the variation in same-sex behaviour, non-shared environment roughly 64 per cent and shared factors, or the family environment, explained 16 per cent.
The study shows that genetic influences are important but modest, and that non-shared environmental factors, which may include factors operating during foetal development, dominate. Importantly, heredity had roughly the same influence as shared environmental factors in women, whereas the latter had no impact on sexual behaviour in men.
Dr Rahman adds: "The study is not without its limitations - we used a behavioural measure of sexual orientation which might be ok to use for men (men's psychological orientation, sexual behaviour, and sexual responses are highly related) but less so for women (who show a clearer separation between these elements of sexuality). Despite this, our study provides the most unbiased estimates presented so far of genetic and non-genetic contributions to sexual orientation."
Queen Mary, University of London
Genetics Current Events and Genetics News RSSResearchers Identify Role of Gene in Tumor Development, Growth and Progression
Virginia Commonwealth University Massey Cancer Center and VCU Institute of Molecular Medicine researchers have identified a gene that may play a pivotal role in two processes that are essential for tumor development, growth and progression to metastasis.
Genetic analysis helps dissect molecular basis of cardiovascular disease
Using highly precise measurements of plasma lipoprotein concentrations determined by nuclear magnetic resonance spectroscopy (NMR), researchers led by Daniel Chasman at Brigham and Women's Hospital and Harvard Medical School in Boston, MA, the Framingham Heart Study in Framingham, and the PROCARDIS consortium in Stockholm, Sweden and Oxford, England performed genetic association analysis across the whole genome among 17,296 women of European ancestry from the Women's Genome Health Study.
It's a gas: New discovery may lead to heartier, high-yielding plants
In a research report published in the November 2009 issue of the journal GENETICS, scientists show how a family of genes (1-aminocyclopropane-1-carboxylate synthase, or ACS genes) are responsible for production of ethylene.
Gene mismatch influences success of bone marrow transplants
A commonly inherited gene deletion can increase the likelihood of immune complications following bone marrow transplantation, an international team of researchers reports in the November 22 advance online issue of Nature Genetics.
Cancer metabolism discovery uncovers new role of IDH1 gene mutation in brain cancer
Agios Pharmaceuticals today announced that its scientists have established, for the first time, that the mutated IDH1 gene has a novel enzyme activity consistent with a cancer-causing gene, or oncogene.
Scientists at UA, collaborating institutions decode maize genome
Scientists from the University of Arizona led by Arizona Genomics Institute director Rod A. Wing and from collaborating institutions have deciphered the complete genetic code of the maize plant for the first time.
Ancestry attracts, but love is blind
People preferentially marry those with similar ancestry, but their decisions are not necessarily based on hair, eye or skin colour.
Scientists unlock clues for tailoring corn plant for food, energy needs
Scientists have long known that the offspring of two inbred strains tend to be superior to both their parents. Now, a team of researchers including a University of Florida geneticist has discovered clues to why that might be the case for one of the most important crops in the world: corn.
Causative gene of a rare disorder discovered by sequencing only protein-coding regions of genome
For the first time, scientists have successfully used a method called exome sequencing to quickly discover a previously unknown gene responsible for a mendelian disorder.
New map of variation in maize genetics holds promise for developing new varieties
A new study of maize has identified thousands of diverse genes in genetically inaccessible portions of the genome. New techniques may allow breeders and researchers to use this genetic variation to identify desirable traits and create new varieties that were not easily possible before.
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