khad
22nd August 2011, 02:22
While this new booming field does not invalidate Darwin, it's interesting because it shows that environmental factors and acquired factors may unlock genetic "switches" that lead to different characteristics. For so long epigenetic research has been stigmatized as debunked trash, but now researchers are coming up with concrete results that show a much more complicated picture of genetic interaction.
http://www.sciencedaily.com/releases/2009/04/090412081315.htm
. Epigenetics: DNA Isn’t Everything
http://images.sciencedaily.com/2009/04/090412081315.jpg (http://images.sciencedaily.com/2009/04/090412081315-large.jpg)
The two pictures show the eyes of two genetically identical flies. The difference in eye colour is determined by epigenetic factors. (Credit: Renato Paro/ETH Zürich)
ScienceDaily (Apr. 13, 2009) — Research into epigenetics has shown that environmental factors affect characteristics of organisms. These changes are sometimes passed on to the offspring. ETH professor Renato Paro does not believe that this opposes Darwin’s theory of evolution.
A certain laboratory strain of the fruit fly Drosophila melanogaster has white eyes. If the surrounding temperature of the embryos, which are normally nurtured at 25 degrees Celsius, is briefly raised to 37 degrees Celsius, the flies later hatch with red eyes. If these flies are again crossed, the following generations are partly red-eyed – without further temperature treatment – even though only white-eyed flies are expected according to the rules of genetics.
Environment affects inheritance
Researchers in a group led by Renato Paro, professor for Biosystems at the Department of Biosystems Science and Engineering (D-BSSE), crossed the flies for six generations. In this experiment, they were able to prove that the temperature treatment changes the eye colour of this specific strain of fly, and that the treated individual flies pass on the change to their offspring over several generations. However, the DNA sequence for the gene responsible for eye colour was proven to remain the same for white-eyed parents and red-eyed offspring.
The concept of epigenetics offers an explanation for this result. Epigenetics examines the inheritance of characteristics that are not set out in the DNA sequence. For Paro, epigenetic mechanisms form an additional, paramount level of information to the genetic information of DNA.
Such phenomena could only be examined in a descriptive manner in the past. Today, it has been scientifically proven, which molecular structures are involved: important factors are the histones, a kind of packaging material for the DNA, in order to store DNA in an ordered and space-saving way. It is now clear that these proteins have additional roles to play. Depending on the chemical group they carry, if they are acetylated or methylated, they permanently activate or deactivate genes. New methods now allow researchers to sometimes directly show which genes have been activated or deactivated by the histones.
Cells have a memory
Epigenetic marks, such as the modifications of the histones, are also important for the specialisation of the body’s cells. They are preserved during cell division and are passed on to the daughter cells. If skin cells divide, more skin cells are created; liver cells form liver cells. In both cell types, all genes are deactivated except the ones needed by a skin or liver cell to be a skin or liver cell, and to function appropriately. The genetic information of the DNA is passed on along with the relevant epigenetic information for the respective cell type.
Paro’s group is researching this cell memory. It is still unclear how the epigenetic markers are passed on to the daughter cells. During cell division, the DNA is doubled, which requires the histones – as the current picture suggests – to break apart. The question is therefore how cellular memory encoded by epigenetic mechanisms survives cell division.
Emerging area of research
A similar question remains for the inheritance of the epigenetic characteristics from parents to offspring. They now know that when the gametes are formed, certain epigenetic markers remain and are passed on to the offspring. The questions, which are currently being researched, are how much and which part of the epigenetic information is preserved and subsequently inherited.
The research is also looking at the influence of various substances from the environment on the epigenetic constitution of organisms, including humans. Diet and epigenetics appear to be closely linked. The most well known example is that of the Agouti mice: they are yellow, fat and are prone to diabetes and cancer. If Agouti females are fed with a cocktail of vitamin B12, folic acid and cholin, directly prior to and during pregnancy, they give birth to mainly brown, slim and healthy offspring. They in turn mainly have offspring similar to themselves.
Contradiction to Darwin?
Environmental factors, which change the characteristics of an individual and are then passed on to its offspring, do not really fit into Darwin’s theory of evolution. According to his theory, evolution is the result of the population and not the single individual. “Passing on the gained characteristics fits more to Lamarck’s theory of evolution”, says Paro.
However, he still does not believe Darwin’s theory of evolution is put into question by the evidence of epigenetics research. “Darwin was 100 percent right”, Paro emphasises. For him, epigenetics complement Darwin’s theory. In his view, new characteristics are generated and passed on via epigenetics, subject to the same mechanisms of evolution as those with a purely genetic origin.http://www.thedailybeast.com/newsweek/2009/09/17/what-alters-our-genes.html
What Alters Our Genes
Sep 17, 2009 8:00 PM EDT
For a time, it was the most famous fraud in biology. From 1906 to 1923, Austrian biologist Paul Kammerer reported remarkable results in experiments with the midwife toad. Highly unusual for an amphibian, Alytes obstetricans mates on land, not water, and the males incubate the eggs on their legs, also on land. But when Kammerer housed midwife toads in a hot, dry terrarium, they spent most of their time in a nearby basin of cool water: they mated there, and mom deposited the eggs there rather than having dad carry them. It was odd enough that so intrinsic (and eponymous) a behavior was so malleable. But Kammerer found something else.
Once the tadpoles grew up—and here is where eyebrows all over European science shot up—they mated and deposited their eggs in water. Dads no longer midwifed eggs, even when they did not live in desert conditions. By the fourth generation, Kammerer reported, male toads even had black "nuptial" pads, a trait water-mating toads have (to grasp a female) but midwife toads do not. Thus did Kammerer demonstrate the inheritance of acquired characteristics, the then- and still-discredited idea that a new behavioral trait (such as reproducing in water) or anatomical one (nuptial pads) can be environmentally induced and passed on to progeny, despite the progeny's never having been exposed to that environment.
Other scientists were dubious. This was before the discovery that DNA is the molecule of heredity, but basic Darwinian and Mendelian theory held that traits are inherited intact from mom and dad, and that the experiences a parent has cannot alter the genetic material in eggs and sperm. Indeed, one of Kammerer's critics found that India ink had been injected into a toad, creating faux nuptial pads; on Aug. 7, 1926, a paper in Nature suggested that Kammerer had committed fraud. Six weeks later, he committed suicide. Arthur Koestler made the saga the subject of his 1971 book, The Case of the Midwife Toad.
Despite attempts here and there to restore his reputation, Kammerer's name became synonymous with science fraud. But in a fascinating new analysis, biologist Alexander Vargas of the University of Chile reaches a far different conclusion: that Kammerer was in fact the discoverer of a phenome-non called epigenetics, in which genes are silenced by—and here I'm simplifying, but only a little—experience. "Rather than being a fraud," says Vargas, "Kammerer could be the true discoverer of non-Mendelian, epigenetic inheritance."
Epigenetics is a booming new field that studies how genes are turned on and off. At the molecular level, that can happen when a cluster of four atoms called a methyl group attaches to a gene, silencing it. What's so fascinating about epigenetics is that it may explain how the life we live can reach into our double helix and alter our traits. For instance, when rat moms lick and groom their pups, it removes DNA silencers from genes that, allowed to sing, cause the pups to become curious and sociable. Epigenetic mechanisms may also explain why identical twins, who inherit identical genes, have different traits, including genetic diseases: the different lives the twins lead cause some disease genes, including those linked to cancer and schizophrenia, to switch off.
It turns out that when eggs, including those of amphibians, spend time in water—as did those of Kammerer's midwife toads—the DNA within undergoes a wave of methylation, turning some genes on and others off. If one such set of genes carries instructions for living on land and midwifing eggs, then turning it off would cause the toad to revert to a classically amphibian way of life, reproducing in water, as Kammerer found. Genes for living on land seem to get "environmentally silenced in early embryos exposed to water," says Vargas, who combed through Kammerer's lab notes and whose analysis appears in the Journal of Experimental Zoology. "It has taken a painfully long time to properly acknowledge that environment can influence inheritance," he told me. "I think academia has discouraged experiments testing environmental modification of inheritance," because the inheritance of acquired characteristics—Lamarckism—drives the self-appointed evolution police crazy.
http://www.sciencedaily.com/releases/2009/04/090412081315.htm
. Epigenetics: DNA Isn’t Everything
http://images.sciencedaily.com/2009/04/090412081315.jpg (http://images.sciencedaily.com/2009/04/090412081315-large.jpg)
The two pictures show the eyes of two genetically identical flies. The difference in eye colour is determined by epigenetic factors. (Credit: Renato Paro/ETH Zürich)
ScienceDaily (Apr. 13, 2009) — Research into epigenetics has shown that environmental factors affect characteristics of organisms. These changes are sometimes passed on to the offspring. ETH professor Renato Paro does not believe that this opposes Darwin’s theory of evolution.
A certain laboratory strain of the fruit fly Drosophila melanogaster has white eyes. If the surrounding temperature of the embryos, which are normally nurtured at 25 degrees Celsius, is briefly raised to 37 degrees Celsius, the flies later hatch with red eyes. If these flies are again crossed, the following generations are partly red-eyed – without further temperature treatment – even though only white-eyed flies are expected according to the rules of genetics.
Environment affects inheritance
Researchers in a group led by Renato Paro, professor for Biosystems at the Department of Biosystems Science and Engineering (D-BSSE), crossed the flies for six generations. In this experiment, they were able to prove that the temperature treatment changes the eye colour of this specific strain of fly, and that the treated individual flies pass on the change to their offspring over several generations. However, the DNA sequence for the gene responsible for eye colour was proven to remain the same for white-eyed parents and red-eyed offspring.
The concept of epigenetics offers an explanation for this result. Epigenetics examines the inheritance of characteristics that are not set out in the DNA sequence. For Paro, epigenetic mechanisms form an additional, paramount level of information to the genetic information of DNA.
Such phenomena could only be examined in a descriptive manner in the past. Today, it has been scientifically proven, which molecular structures are involved: important factors are the histones, a kind of packaging material for the DNA, in order to store DNA in an ordered and space-saving way. It is now clear that these proteins have additional roles to play. Depending on the chemical group they carry, if they are acetylated or methylated, they permanently activate or deactivate genes. New methods now allow researchers to sometimes directly show which genes have been activated or deactivated by the histones.
Cells have a memory
Epigenetic marks, such as the modifications of the histones, are also important for the specialisation of the body’s cells. They are preserved during cell division and are passed on to the daughter cells. If skin cells divide, more skin cells are created; liver cells form liver cells. In both cell types, all genes are deactivated except the ones needed by a skin or liver cell to be a skin or liver cell, and to function appropriately. The genetic information of the DNA is passed on along with the relevant epigenetic information for the respective cell type.
Paro’s group is researching this cell memory. It is still unclear how the epigenetic markers are passed on to the daughter cells. During cell division, the DNA is doubled, which requires the histones – as the current picture suggests – to break apart. The question is therefore how cellular memory encoded by epigenetic mechanisms survives cell division.
Emerging area of research
A similar question remains for the inheritance of the epigenetic characteristics from parents to offspring. They now know that when the gametes are formed, certain epigenetic markers remain and are passed on to the offspring. The questions, which are currently being researched, are how much and which part of the epigenetic information is preserved and subsequently inherited.
The research is also looking at the influence of various substances from the environment on the epigenetic constitution of organisms, including humans. Diet and epigenetics appear to be closely linked. The most well known example is that of the Agouti mice: they are yellow, fat and are prone to diabetes and cancer. If Agouti females are fed with a cocktail of vitamin B12, folic acid and cholin, directly prior to and during pregnancy, they give birth to mainly brown, slim and healthy offspring. They in turn mainly have offspring similar to themselves.
Contradiction to Darwin?
Environmental factors, which change the characteristics of an individual and are then passed on to its offspring, do not really fit into Darwin’s theory of evolution. According to his theory, evolution is the result of the population and not the single individual. “Passing on the gained characteristics fits more to Lamarck’s theory of evolution”, says Paro.
However, he still does not believe Darwin’s theory of evolution is put into question by the evidence of epigenetics research. “Darwin was 100 percent right”, Paro emphasises. For him, epigenetics complement Darwin’s theory. In his view, new characteristics are generated and passed on via epigenetics, subject to the same mechanisms of evolution as those with a purely genetic origin.http://www.thedailybeast.com/newsweek/2009/09/17/what-alters-our-genes.html
What Alters Our Genes
Sep 17, 2009 8:00 PM EDT
For a time, it was the most famous fraud in biology. From 1906 to 1923, Austrian biologist Paul Kammerer reported remarkable results in experiments with the midwife toad. Highly unusual for an amphibian, Alytes obstetricans mates on land, not water, and the males incubate the eggs on their legs, also on land. But when Kammerer housed midwife toads in a hot, dry terrarium, they spent most of their time in a nearby basin of cool water: they mated there, and mom deposited the eggs there rather than having dad carry them. It was odd enough that so intrinsic (and eponymous) a behavior was so malleable. But Kammerer found something else.
Once the tadpoles grew up—and here is where eyebrows all over European science shot up—they mated and deposited their eggs in water. Dads no longer midwifed eggs, even when they did not live in desert conditions. By the fourth generation, Kammerer reported, male toads even had black "nuptial" pads, a trait water-mating toads have (to grasp a female) but midwife toads do not. Thus did Kammerer demonstrate the inheritance of acquired characteristics, the then- and still-discredited idea that a new behavioral trait (such as reproducing in water) or anatomical one (nuptial pads) can be environmentally induced and passed on to progeny, despite the progeny's never having been exposed to that environment.
Other scientists were dubious. This was before the discovery that DNA is the molecule of heredity, but basic Darwinian and Mendelian theory held that traits are inherited intact from mom and dad, and that the experiences a parent has cannot alter the genetic material in eggs and sperm. Indeed, one of Kammerer's critics found that India ink had been injected into a toad, creating faux nuptial pads; on Aug. 7, 1926, a paper in Nature suggested that Kammerer had committed fraud. Six weeks later, he committed suicide. Arthur Koestler made the saga the subject of his 1971 book, The Case of the Midwife Toad.
Despite attempts here and there to restore his reputation, Kammerer's name became synonymous with science fraud. But in a fascinating new analysis, biologist Alexander Vargas of the University of Chile reaches a far different conclusion: that Kammerer was in fact the discoverer of a phenome-non called epigenetics, in which genes are silenced by—and here I'm simplifying, but only a little—experience. "Rather than being a fraud," says Vargas, "Kammerer could be the true discoverer of non-Mendelian, epigenetic inheritance."
Epigenetics is a booming new field that studies how genes are turned on and off. At the molecular level, that can happen when a cluster of four atoms called a methyl group attaches to a gene, silencing it. What's so fascinating about epigenetics is that it may explain how the life we live can reach into our double helix and alter our traits. For instance, when rat moms lick and groom their pups, it removes DNA silencers from genes that, allowed to sing, cause the pups to become curious and sociable. Epigenetic mechanisms may also explain why identical twins, who inherit identical genes, have different traits, including genetic diseases: the different lives the twins lead cause some disease genes, including those linked to cancer and schizophrenia, to switch off.
It turns out that when eggs, including those of amphibians, spend time in water—as did those of Kammerer's midwife toads—the DNA within undergoes a wave of methylation, turning some genes on and others off. If one such set of genes carries instructions for living on land and midwifing eggs, then turning it off would cause the toad to revert to a classically amphibian way of life, reproducing in water, as Kammerer found. Genes for living on land seem to get "environmentally silenced in early embryos exposed to water," says Vargas, who combed through Kammerer's lab notes and whose analysis appears in the Journal of Experimental Zoology. "It has taken a painfully long time to properly acknowledge that environment can influence inheritance," he told me. "I think academia has discouraged experiments testing environmental modification of inheritance," because the inheritance of acquired characteristics—Lamarckism—drives the self-appointed evolution police crazy.