Showing posts with label DNA. Show all posts
Showing posts with label DNA. Show all posts

October 23, 2018

DNA Differences May Be Linked to Having Same Sex Partners

 For some people, choosing a same-sex partner may be in their DNA.
In a large study of more than 490,000 men and women in the United States, United Kingdom and Sweden, researchers discovered four genetic variants that occur more often in people who indicated on questionnaires that they had had same-sex sexual partners. Andrea Ganna, a geneticist at the Broad Institute of MIT and Harvard reported the results October 19 at the annual meeting of the American Society of Human Genetics. Two of the variants were specific to men’s sexual partner choice. The other two influence sex partner choice for both men and women.

Collectively, the DNA differences explained only 8 to 12 percent of the heritability of having same-sex partners. “There is no gay gene,” Ganna said, “but rather non-heterosexuality is influenced by many tiny-effect genetic factors.”

The new study is an advance over previous attempts to find “gay genes,” says J. Michael Bailey, a psychologist at Northwestern University in Evanston, Ill., who was not involved in the new work. The study’s size is its main advantage, Bailey says. “It’s huge. Huge.”

Researchers examined DNA data from more than 400,000 participants in the U.K. Biobank and more than 69,000 people who had their DNA tested by the consumer testing company 23andMe. People who have given their DNA data to those research projects also answered a battery of questions, including ones about whether they had ever had a partner of the same sex and how many sexual partners they have had. The findings were replicated with data from three other studies, including one from Sweden. Findings from such large studies are more likely to be replicated than the small studies in the past, Bailey says. Researchers have “really gotten these studies down now and if they find things, it’s pretty sure that they’re true.”
Previous sexual orientation genetic studies, including some Bailey was involved in, may also have suffered from bias because they relied on volunteers. People who offer to participate in a study, without being randomly selected, may not reflect the general population, he says. This study includes both men and women and doesn’t rely on twins, as many previous studies have, he says. “It’s a huge advance … but it doesn’t tell us everything we need to know.”
For instance, the study doesn’t address people’s attraction to members of the same sex. Some people who have had sex with a same-sex partner don’t consider themselves gay and aren’t exclusively attracted to people of the same sex, Bailey says. He calls the study’s definition of non-heterosexual behavior as having ever had a same-sex partner “a flawed, but not ridiculous indicator of sexual orientation.”

Men in the new study who said they have had same-sex partners, tended to be more exclusively homosexual than women were, Ganna and colleagues found. But people of both sexes ran the gamut of sexual orientations. In the U.K. Biobank dataset, for example, younger people reported having same-sex partners more often than older people did, probably because homosexual activity was illegal in the United Kingdom until 1967.
This is not the only complex human phenomenon for which we see a genetic influence without a great understanding of how that influence works.
— Lisa Diamond

This is the first DNA difference ever linked to female sexual orientation, says Lisa Diamond, a psychologist at the University of Utah in Salt Lake City who studies the nature and development of same-sex sexuality. The results are consistent with previous studies suggesting genetics may play a bigger role in influencing male sexuality than female sexuality. It’s not unusual for one sex of a species to be more fluid in their sexuality, choosing partners of both sexes, Diamond says. For humans, male sexuality may be more tightly linked to genes.

But that doesn’t mean that genes control sexual behavior or orientation. “Same-sex sexuality appears to be genetically influenced, but not genetically determined,” Diamond says. “This is not the only complex human phenomenon for which we see a genetic influence without a great understanding of how that influence works.” Other complex human behaviors, such as smoking, alcohol use, personality and even job satisfaction all have some genetic component.
Previous research had suggested that genes influencing sexual orientation were located on the X chromosome (SN: 11/4/95. p. 295; SN: 7/7/93, p. 37). But Ganna and colleagues found no evidence that the X chromosome is involved in partner choice, he said.

Instead, the researchers found genetic variants known as single nucleotide polymorphisms, or SNPs, located on four other chromosomes. SNPs are naturally occurring spots in the DNA where some people have one DNA base, or letter, and other people have another. The variants didn’t change any genes, but were found near some genes that may be involved.

For instance, a variant on chromosome 15 linked to men having sex with men is also associated with male pattern baldness. Another variant in the study is near the ORA51A gene on chromosome 11, which is involved in the ability to smell certain chemicals. That’s interesting because smell has been linked to attraction before (SN Online: 3/12/15), Ganna said.  The researchers don’t yet know exactly which genes are involved in mate choice or exactly how they influence behavior.

One mystery the discovery may help solve is how genetic variants associated with having same-sex partners could persist across generations. Such variants would presumably get weeded out if men and women who have sex with people of the same sex don’t have children or have fewer children than the average person.

 Its not a choice but an orientation

In the new study, the more exclusively homosexual partners men had, the fewer children they had; up to 80 percent fewer children than heterosexual men. In a preliminary conference report, the researchers suggested that the variants are associated with heterosexuals having more sexual partners than usual, and that heterosexual men with some of the variants are more attractive than those without. Those traits would give heterosexuals a greater chance to pass the variants on to offspring, keeping those DNA differences in the gene pool. Ganna did not discuss those possibilities from the podium. 

Diamond disagrees that researchers need to find a mechanism to explain the persistence of genetic variants linked to homosexuality. Same-sex behavior has never completely supplanted heterosexual mating in any species studied, she says. Only in the last 50 years have gay people tended to exclusively choose same-sex partners, she says. “You don’t really need some reproductive benefit for same-sex sexuality, because same-sex sexuality almost never occurs exclusively. Individuals with that predisposition have been mating and reproducing with heterosexual partners for millennia, and that’s why it’s still in the gene pool.”

October 13, 2015

New DNA Evidence Between gay Men and their Twins Should Give Haters No Comfort


For men, new research suggests that clues to sexual orientation may lie not just in the genes, but in the spaces between the DNA, where molecular marks instruct genes when to turn on and off and how strongly to express themselves.

On last Thursday, UCLA molecular biologist Tuck C. Ngun reported that in studying the genetic material of 47 pairs of identical male twins, he has identified "epigenetic marks" in nine areas of the human genome that are strongly linked to male homosexuality.

In individuals, said Ngun, the presence of these distinct molecular marks can predict homosexuality with an accuracy of close to 70%.
That news, presented at the 2015 meeting of the American Society of Human Genetics on Thursday, may leave the genetically uninitiated scratching their heads.

But experts said the results -- as yet unpublished in a peer-reviewed journal -- offer preliminary new evidence that a man's genetic inheritance is only one influence on his sexual orientation. Through the epigenome, the results suggest, some facet of life experience likely also primes a man for same-sex attraction.
Over a person's lifetime, myriad environmental factors -- nutrition, poverty, a mother's love, education, exposure to toxic chemicals -- all help shape the person he will become.

Researchers working in the young science of epigenetics acknowledge they are unsure just how an individual's epigenome is formed. But they increasingly suspect it is forged, in part, by the stresses and demands of external influences. A set of chemical marks that lies between the genes, the epigenome changes the function of genetic material, turning the human body's roughly 20,000 protein-coding genes on or off in response to the needs of the moment.
Geneticists suggest that together, the human genome and its epigenome reflect the interaction of nature and nurture -- both our fixed inheritance and our bodies' flexible responses to the world -- in making us who we are.

Ngun's study of twins doesn't reveal how or when a male takes on the epigenomic marks that distinguish him as homosexual. Many researchers believe that a person's eventual sexual preferences are shaped in the uterus, by hormonal shifts during key stages of fetal brain development.
By imprinting themselves on the epigenome, though, environmental influences may powerfully affect how an individual's genes express themselves over the course of his life. Ngun's findings suggest they may interact with genes to nudge sexual orientation in one direction or the other.

"The relative contributions of biology versus culture and experience in shaping sexual orientation in humans continues to be debated," said University of Maryland pharmacology professor Margaret M. McCarthy, who was not involved in the current study. "But regardless of when, or even how, these epigenetic changes occur," she added, the new research "demonstrates a biological basis to partner preference."

To find the epigenomic markers of male homosexuality, Ngun, a postdoctoral researcher at UCLA's Geffen School of Medicine, combed through the genetic material of 47 sets of identical male twins. Thirty-seven of those twin sets were pairs in which one was homosexual and the other was heterosexual. In 10 of the pairs studied, both twins identified as homosexual.

In identical twins, DNA is shared and overlaps perfectly. But the existence of twin pairs in which one is homosexual and the other is not offers strong evidence that something other than DNA alone influences sexual orientation. Ngun and his colleagues looked for patterns of DNA methylation -- the chemical process by which the epigenome is encoded -- to identify the missing factor in partner preference.

Their analysis generated a dataset far too large for a team of humans to make sense of. So they unleashed a machine learning algorithm on the data to search for regularities that distinguished the epigenomes of homosexual twin-pairs from twins in which only one was homosexual.

In nine compact regions scattered across the genome, they found patterns of epigenomic differences that would allow a prediction far more accurate than a random guess of an individual's sexual orientation, Ngun reported Thursday.

McCarthy and other experts cautioned that the discovery of epigenomic marks suggestive of homosexuality is a far cry from finding the causes of sexual preference.

The distinctive epigenomic marks observed by Ngun and his colleagues could result from some other biological or lifestyle factor common to homosexual men but unrelated to their sexuality, said University of Utah geneticist Christopher Gregg. They could correlate with homosexuality but have nothing to do with it.

“Epigenetic marks are the consequence of complex interactions between the genetics, development and environment of an individual," said University of Cambridge geneticist Eric Miska. "Simple correlations -- if significant -- of epigenetic marks of an individual with anything from favorite football player to disease risk does not imply a causal relationship or understanding.”

One longtime researcher in the field of sexual orientation praised Ngun’s use of identical twins as a means of teasing apart the various biological factors that influence the trait.

“Our best guess is that there are genes” that affect a man’s sexual orientation “because that’s what twin studies suggest,” said Northwestern University psychologist J. Michael Bailey, who  has explored a range of physiological markers that point to homosexuality’s origins in the womb. But the existence of identical twin pairs in which only one is homosexual “conclusively suggest that genes don’t explain everything,” Bailey added.

While Ngun’s research needs to be replicated in larger studies of twins, it advances the fitful process of better understanding how — and when — a boy’s sexual orientation develops, Bailey said.

The study by Dr Tuck C Ngun and his team at the University of California created an algorithm which, by measuring small genetic modifications which occur after birth,could guess the sexual orientation of males with up to 70 percent accuracy. This indicates that environmental factors have a significant influence on human sexuality, both heterosexual and homosexual. 
But how much influence is still unclear. We already have plenty of previous research that points to major biological influences on sexual orientation. This includes "gay gene" studies that have identified the Xq28 markeron the X chromosome as associated with homosexuality. Other research has found that among identical twins where one brother is gay the likelihood of the other brother also being gay is much greater than the incidence of homosexuality in the general population. 
Research has further revealed differences between gay and non-gay men in physical attributes caused by hormonal influences in the womb. These include differences in physique, brain structure, finger lengths, penis size (gay men tend to be better endowed than straight men), and the age of puberty (on average gay men mature earlier than heterosexual men). 
While all these studies have been disputed to varying degrees by fellow scientists - as no doubt will Dr Ngun’s research - the preponderance of scientific evidence nevertheless does point to biological factors as being prime influences on sexual orientation. 
Several studies have suggested a link between sexual orientation and digit ratio  Photo:

September 4, 2014

DNA Clears Two Men of Raping Child and Murder, after 31 yrs in jail

 Henry Lee McCollum had barely slept in days, terrified that his dream of 31 years — being released from North Carolina’s death row — might not come true.
But finally on Wednesday morning, after one more night of delays, he was driven out of the concertina-wire gates of the central prison in Raleigh and to the waiting arms of his parents.
“I just thank God I’m out of this place,” Mr. McCollum, 50, said. “Now I want to eat, I want to sleep, and I want to wake up tomorrow and see that this is real.”

Despite a judge’s order on Tuesday overturning their conviction in the 1983 rape and murder of a child, Mr. McCollum and his half brother, Leon Brown, remained in custody overnight as officials processed the paperwork for their release. Mr. McCollum finally left the prison around 9:42 a.m. on Wednesday. Mr. Brown, 46, who was serving a life sentence, was released from prison around 1 p.m. He walked out of the prison gates in Maury, N.C., 80 miles east of Raleigh, and was embraced by family members. “God is good all the time,” he said.


Henry Lee McCollum, with his back to the camera, and his father, James McCollum, after being released from Central Prison in Raleigh, N.C., on Wednesday.CreditJonathan M. Katz for The New York Times

When Mr. McCollum was finally released here, his father and stepmother, James and Priscilla McCollum, began to cry and shout for joy as the son they call Buddy stepped out in a houndstooth jacket, khaki pants and slate blue tie he had been given by the lawyers who helped secure his release. The legal team, from the Center for Death Penalty Litigation, began weeping and hugging as well. Standing a free man in fresh air for the first time in his adult life, Mr. McCollum swatted away gnats as he faced a phalanx of television cameras. He told the reporters that his faith in God had sustained him through years of fear that the legal system that had wrongly incarcerated him would also wrongly take his life.
Mr. McCollum also spoke of the 152 men still on death row in the state prison, whom he called his family.
“You’ve still got innocent people on North Carolina death row,” he said. “Also you’ve got some guys who should not have gotten the death penalty. That’s wrong. You got to do something about those guys.”
Finally free, Mr. McCollum, who like Mr. Brown is mentally disabled — Mr. Brown’s I.Q. in tests has registered as low as 51 — faces the challenge of his life: learning to live in a world he has not experienced since he was a teenager three decades ago. On death row, Mr. McCollum was never allowed to open a door, turn on the light switch or use a zipper. He never had a cellphone and until last week had not used the Internet. (He excitedly told his stepmother about his first use of Google Maps days ago, when he saw pictures of her house.)
When he got into the family car, a navy Dodge Journey, he sheepishly slipped the beige shoulder belt around his neck and let it hang, unsure of how to use it.


Mr. McCollum sat in court on Tuesday. CreditChuck Liddy/The News & Observer, via Associated Press

Mr. McCollum will also have to get used to life in a state he hardly knows. Though two-thirds of his life have been spent behind North Carolina plexiglass and bars, he grew up in Jersey City and had only been visiting his mother and relatives for a short time when he and his half brother were arrested in 1983. (The family is still spread out across North Carolina and New Jersey; several relatives came down from New Jersey to attend the hearing and be present when the men were released.) Far from the New York metropolitan area of his youth, Mr. McCollum will now be adjusting to life in a North Carolina town with a smaller population than the death row he just left behind. The lawyers with the Center for Death Penalty Litigation said that there was no formal compensation or assistance to help exonerated prisoners reintegrate into society.
“It’s not like being on probation or parole. It’s just — good luck,” said Gerda Stein, the center’s director of public information. She added that the legal team’s own social worker was coordinating with prison social workers and psychologists to help find services for the men in the towns they are returning to.
The lawyers are also considering asking for a “pardon of innocence” — a declaration affirming that a person was erroneously convicted and imprisoned — from Gov. Pat McCrory. If granted, it would allow both men to seek compensation from the state. The family, which had been focused on securing the men’s release, did not immediately have plans to seek redress from the government, Ms. Stein said.
Last December, Mr. McCrory granted a pardon of innocence to LaMonte Burton Armstrong of Chapel Hill after a newly examined palm print from the crime scene showed he had been wrongly convicted of the 1988 murder of a North Carolina A&T professor. Mr. Armstrong had been released from prison in March 2013 and requested the pardon that following June, according to the governor’s office.
For now Mr. McCollum’s father, James, said he wanted to get his son back home to the small town of Bolivia, near Cape Fear.
“We’re going to go home to Bolivia, take a shower,” he said. “Then I’m going to say: ‘Do you want to go fishing? I’m going to teach you how to fish.’ ” As he got into the driver’s seat to leave, James McCollum put on a hat that said “Jesus Is My Boss.”

New york Times

November 16, 2013

Do you Know Where Your Fido Comes From?

8,500-year-old dog remains from Koster site, Greene County, IllinoisThe story of how dogs came to be so closely associated with humans is open to debate

The results of a DNA study suggest that dogs were domesticated in Europe.
No-one doubts that "man's best friend" is an evolutionary off-shoot of the grey wolf, but scientists have long argued over the precise timing and location for their emergence.
The new research, based on a genetic analysis of ancient and modern dog and wolf samples, points to a European origin at least 18,000 years ago.
Olaf Thalmann and colleagues report the investigation in Science magazine.
It adds a further layer of complexity to the story.
Earlier DNA studies have suggested the modern pooch - in all its shapes and sizes - could track its beginnings back to wolves that attached themselves to human societies in the Middle East or perhaps in East Asia as recently as 15,000 years ago.
The problem with these claims is that palaeontologists have found fossils of distinctly dog-looking animals that are 30,000 years old or more.
Dr Thalmann, from Finland's University of Turku, and his team, have had another go at trying to sort through the conflicting DNA evidence.
They compared genetic sequences from a wide range of ancient animals - both dogs and wolves - with material taken from living canines - again, from both dogs and wolves.
This analysis reveals modern dogs to be most closely related to ancient European wolves or dogs - not to any of the wolf groups from outside Europe, nor even to modern European wolves (suggesting the link is with old European wolves that are now extinct). And because the dog remains used in the research are dated to be more than 18,000 years old, it indicates a timing for domestication that is much older than some researchers have previously argued.
If correct, it means dogs started to diverge from wolf populations when humans had yet to settle into fixed, agricultural communities and were still hunting and gathering.
It is possible there were wolves that would follow these hunters, may be at a distance at first, living off the scraps and discards from the humans' big-game kills such as mammoth, before eventually being incorporated into the human groups as they became less wary.
"You can see how wolves benefitted from living near humans because they got these carcases, but humans too would have benefitted," said Dr Thalmann.
"You have to remember that 18,800-32,000 years ago, Europe had much bigger predators than even wolves, such as bears and hyenas. And you can imagine that having wolves living close to you might be a very useful alarm system," he told BBC News. "It's a plausible scenario for the origin of the domestication of dogs."
The latest study is unlikely to be the last word on the subject, however.
Using DNA - and the subtle changes it undergoes over time - to examine animal origins and relationships is a very powerful tool, but far from fool-proof.
One of the problems scientists have is that dog populations have become very mixed over time, as a result of being moved around by their human owners. This complicates the genetic signal.
The difficulty is further amplified by the fact that some dogs have at times also clearly back-bred with wild wolves. Teasing all this apart is very difficult.
A resolution will require more sampling and more analysis, particularly of the core, or nuclear, DNA of ancient animals.
This and many of the previous studies have relied on so-called mitochondrial DNA (mtDNA), a small sub-packet of genetic material in cells that, although incredibly useful, does not represent the fullest information possible.
The larger nuclear DNA material could provide the more compelling answers but it is far harder to retrieve, especially in very old bones or fossils. A number of research groups around the world are trying, though.

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