Mosaicism in iris color not a problem — compared, say, to mosaicism in kidneys
When Meriel M. McEntagart, a geneticist at St. George’s University of London, met this family in May 2012, she suspected that three of the children had a rare genetic disorder called Smith-Magenis syndrome…Dr. McEntagart confirmed that diagnosis with a genetic test. The children were all missing an identical chunk of a gene known as RAI1.
One of the children had a different father from the other two, and so the mother could be the only source of their altered gene. But when Dr. McEntagart ran a standard blood test on the mother, the results were not nearly so straightforward: The woman had a normal version of RAI1.
Dr. McEntagart and her colleagues suspected that the answer to this puzzle was that the mother was a genetic mosaic.
We tend to think of ourselves as having just one set of genetic material, which exists in identical form in every one of our cells. But sometimes, people have two or more significantly different genomes. As our cells divide, some may go through a major mutation. So some individuals end up with groups of cells that have very different DNA from the rest of them.
Dr. McEntagart said that she suspected that the mother she encountered had a normal version of RAI1 in some cells but an altered version in other cells, including her eggs.
“We wanted to understand if there was a way to demonstrate that she was a mosaic,” Dr. McEntagart said…
In a study released Thursday in the American Journal of Human Genetics, the Baylor team and its colleagues describe the biggest search for cases in which mosaic parents passed down disease-causing mutations to their children. It turns out to be far from a fluke…
Michael Snyder, a geneticist at Stanford University who was not involved in the study, said it showed that mosaicism could have a significant effect on not just people’s own health, but on their children as well.
Having developed a method for detecting mosaic parents, the scientists decided to conduct a larger study to see how common mosaicism is. They began searching for families that would be willing to participate. Each family had to have a child that had a genetic disorder caused by the deletion of some DNA. And they had to have taken a standard genetic test that had failed to find the deletion in either parent’s genes.
Eventually, the scientists were able to study 100 families. They searched for cases in which the parents were mosaics and had the same mutation as their children.
“We thought going into this study we’d find maybe one or two if we were lucky,” said Ian M. Campbell, the lead author of the study. “And then we found four.”
Mr. Campbell and his colleagues were surprised to find that many mosaic parents. And they suspect that the true number of mosaics among the 100 families was even higher. For one thing, their method lets them detect only genetic deletions, but other kinds of mutations can cause genetic disorders, too.
James R. Lupski, another co-author on the study, points to a second limitation of the study. “It only tells you what you see in the blood,” he said. If the scientists could have examined muscle or other tissues, they might have found even more mosaic cells.
The results suggest that some people can have serious genetic diseases without any symptoms. That’s because they have the defective version of a gene in only some of their cells, and their other cells compensate for them.
But such people are unknowingly at risk of having children with full-blown versions of their diseases, if the mutation appears in their reproductive cells. Dr. Lupski said that as technology improved, clinical geneticists should test people for this hidden risk.
“Couples are going to want some answers,” he said.
Another benefit of modern science – unfortunately rejected by some. Equipping a happy couple to make an informed decision about whether or not to bring someone into life that may be one of unwarranted difficulty and pain is at a minimum an opportunity for choice.
Modern chickens are descended primarily from the red junglefowl
The meat and eggs of domestic chickens are a source of protein for billions. Yet how and when the birds were domesticated remains a mystery. The answers to these questions could reveal a wealth of information about the genetics of domestication, as well as human behaviour, and how we can improve our husbandry of the birds.
In a bid to learn more about the chicken and its lineage, the UK government is funding a £1.94-million (US$3.3-million) effort to determine how the chicken went from being a wild fowl roaming the jungles of southeast Asia several thousand years ago to one of the world’s most abundant domesticated animals. The Cultural and Scientific Perceptions of Human–Chicken Interactions project — ‘Chicken Coop’ for short — will examine human history from the perspective of the fowl…
But no domestic animal has been moulded and remoulded by humans as extensively as chickens, says Greger Larson, an evolutionary geneticist. The animals have been bred for eating, egg-laying and fighting. And in the case of one particularly vocal breed, the creatures have even been strapped to the masts of Polynesian boats to act as foghorns. “Chickens are polymaths,” he says…
Because…mutations are so common in contemporary chickens, Larson’s team and others assumed that humans influenced these traits through selective breeding early in the course of domestication. But DNA from chickens recovered at archaeological sites across Europe, spanning the period from around 280 bc to ad 1800, has turned that idea on its head. In an analysis published last month, Larson’s team reported that none of 25 ancient chickens would have had yellow legs, and that just 8 out of 44 birds carried two copies of the TSHR variant…universal in modern breeds. So even 200 years ago, chickens may have been very different from those we know today.
With the help of other Chicken Coop members, Larson is also trying to get to grips with the wider evolutionary forces that shaped modern chickens. He hopes to determine why, for instance, chickens have not been wiped out by disease. This might have been expected because their very rapid selection — much of which has taken place since 1900 — should have led to inbreeding and, by whittling down immune genes, a reduced ability to respond to infections.
I love chicken almost as much as I love pork. I wasn’t raised with any religious or philosophical beliefs that inhibit the consumption of animal protein. So, no problem there. :)
Until modern science comes up with a sound reason to avoid healthfully-raised specimens of foods my progenitors used to catch in the wild – and eat – I will continue to do the same. Though restricting my hunt to the aisles of markets of all types, from chain stores to local farmers.
Electronic cigarettes can change gene expression in a similar way to tobacco, according to one of the first studies to investigate the biological effects of the devices.
Presented at the American Association for Cancer Research annual meeting on 6 April in San Diego, California, the research looked at human bronchial cells that contained some mutations found in smokers at risk of lung cancer. The cells were immortalized, grown in culture medium that had been exposed to e-cigarette vapour and their gene expression profiled.
The researchers found that the cells grown in medium exposed to the vapour of e-cigarettes showed a similar pattern of gene expression to those grown in a medium exposed to tobacco smoke…
The changes are not identical, says study researcher Avrum Spira, who works on genomics and lung cancer at Boston University in Massachusetts. But “there are some striking similarities”, he says. The team is now evaluating whether the alterations mean that cells behave more like cancer cells in culture.
I don’t doubt the companies making a buck from this latest tobacco “substitute” will fight to the death to protect their profits. Your death. Their profits.
The price of silent mutations
Everyone has on average 400 flaws in their DNA, a UK study suggests…Most are “silent” mutations and do not affect health, although they can cause problems when passed to future generations…Others are linked to conditions such as cancer or heart disease, which appear in later life, say geneticists.
The evidence comes from the 1,000 Genomes project, which is mapping normal human genetic differences, from tiny changes in DNA to major mutations.
In the study, 1,000 seemingly healthy people from Europe, the Americas and East Asia had their entire genetic sequences decoded, to look at what makes people different from each other, and to help in the search for genetic links to diseases.
The new research, published in The American Journal of Human Genetics, compared the genomes of 179 participants, who were healthy at the time their DNA was sampled, with a database of human mutations developed at Cardiff University.
It revealed that a normal healthy person has on average about 400 potentially damaging DNA variations, and two DNA changes known to be associated with disease.
“Ordinary people carry disease-causing mutations without them having any obvious effect,” said Dr Chris Tyler-Smith, a lead researcher on the study from the Wellcome Trust Sanger Institute, Cambridge.
He added: “In a population there will be variants that have consequences for their own health.”
The research gives an insight into the “flaws that make us all different, sometimes with different expertise and different abilities, but also different predispositions in diseases,” said Prof David Cooper of Cardiff University, the other lead researcher of the study.
“Not all human genomes have perfect sequences,” he added. “The human genome is packed with pervasive, architectural flaws.”
It has been known for decades that all people carry some genetic mutations that appear to cause little or no harm. Many are only damaging if they are passed on to children who inherit another copy of the faulty gene from the other parent.
In others – around one in ten of those studied – the mutation causes only a mild condition, appears to be inactive, or does not manifest itself until later life.
Databases of human mutations, like the one at Cardiff University, will have increasing importance in the future, as we move into the era of personalised medicine…But as DNA sequencing becomes more widespread, ethical dilemmas will arise about what to tell people about their genes, especially when many risks are uncertain.
We all understand the range of dead ends available for time-wasting by ethicists. Especially those with one or another superstition to justify. I come down – in advance – on the side of the simplest and most democratic premise: knowledge is always useful. I don’t care if someone decides if it’s scary or silly – I have the right to know.
Photographs of variously mutated brown trout were relegated to an appendix of a scientific study commissioned by the J. R. Simplot Company, whose mining operations have polluted nearby creeks in southern Idaho. The trout were the offspring of local fish caught in the wild that had been spawned in the laboratory. Some had two heads; others had facial, fin and egg deformities.
Yet the company’s report concluded that it would be safe to allow selenium — a metal byproduct of mining that is toxic to fish and birds — to remain in area creeks at higher levels than are now permitted under regulatory guidelines. The company is seeking a judgment to that effect from the Environmental Protection Agency. After receiving a draft report that ran hundreds of pages, an E.P.A. review described the research as “comprehensive” and seemed open to its findings, which supported the selenium variance for Simplot’s Smoky Canyon mine.
But when other federal scientists and some environmentalists learned of the two-headed brown trout, they raised a ruckus, which resulted in further scientific review that found the company’s research wanting.
Now, several federal agencies, an array of environmental groups and one of the nation’s largest private companies are at odds over selenium contamination from the Idaho phosphate mine, the integrity of the company’s research, and what its effect will be on future regulatory policy.