Field of reference: Biology
Description: A summary of 2.5hr lecture by Dr. Lipton on the influence of the environment on human Biology
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שייך לקטגוריות 3. השפעת הסביבה = חוק | להשאיר תגובה | |
Field of reference: Biology
Description: Video Interview: speaks of experiments for determining the influence of the environment on cells in the beginning of the talk
>"A very simple experiment that is very profound for us today is: If i took my dish, a plastic petry dish with cells in it, and moved it from a healthy environment to a less than healthy environment the cells get sick. And if I were a doctor of cells, well, you might say "what kind of drugs would you give these cells?"... It turns out, no, you don't give the cells any drugs. You just take the dish from the bad environment, put it back into a good environment, and the cells will innately, naturally, come back to health again."
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שייך לקטגוריות 3. השפעת הסביבה = חוק | להשאיר תגובה | |
Field of reference: Biology
>"Epigenetics in the broad sense refers to two kinds of inheritance. (1) Cellular epigenetic inheritance through mitotic cells and transgenerational epigenetic inheritance through meiotic cells. Transgenerational heredity of DNA methylation has been observed in unicellular organisms, plants, and mammals, suggesting that transgenerational epigenetic inheritance may be more prevalent than often suspected (Jablonka & Raz 2009). (2) Hereditary effects that by-pass the germline, for example through early developmental inputs that lead to regeneration of previous developmental conditions (e.g., hormonal and neural conditions) and other forms of phenotypic transmission, such as the transmission of symbionts and parasites, e.g., gut bacteria (Jablonka & Raz 2009)."
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שייך לקטגוריות 3. השפעת הסביבה = חוק | להשאיר תגובה | |
Field of reference: Biology
Description: The appearance of a particular organ is the product of the genotype and the epigenotype, reacting with the external environment’.
>"Historically, the term ‘epigenetics’ is attributed to Conrad Waddington (1905–75) who in the late 1930s remarked ‘It is, surely, obvious that the fertilized egg contains constituents which have definite properties which allow only a certain limited number of reactions to occur; in so far as this is true, one may say that development proceeds on a basis of the “preformed” qualities of the fertilized egg. But equally it is clear that the interaction of these constituents gives rise to new types of tissue and organ which were not present originally, and in so far development must be considered as “epigenetic” ’ [1]. He further remarked that ‘One might say that the set of organizers and organizing relations to which a certain piece of tissue will be subject during development make up its “epigenetic constitution” or “epigenotype”; then the appearance of a particular organ is the product of the genotype and the epigenotype, reacting with the external environment’."
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שייך לקטגוריות 3. השפעת הסביבה = חוק | להשאיר תגובה | |
Field of reference: Biology
Description: Conrad Waddington an embryologist used a metaphor called an "epigenetic landscape" describing the development of an individual organism, or part of, such as an organ. cell. or tissue and the effects of development according to its reactions with the external environment.
>"Epigenetics is the study of reversible heritable changes in gene function that occur without a change in the sequence of nuclear DNA. It is also the study of the processes involved in the unfolding development of an organism. In both cases, the object of study includes how gene regulatory information that is not expressed in DNA sequences is transmitted from one generation to the next – that is “in addition to” the genetic information encoded in the DNA. In its simplest manifestation, epigenetics is defined as any genetic mechanism that results in phenotypic variation without altering the base-pair nucleotide sequence of the genes. (3)Waddington used an important visual metaphor to describe the development of an individual organism –or part of an organism, such as an organ, tissue or even a specific cell. He likened it to a ball rolling down an undulating, dissected landscape predetermined by the genetic architecture that lay underneath. This he called an epigenetic landscape. This epigenetic landscape is a metaphor for how gene regulation modulates development. One is asked to imagine a number of marbles rolling down a hill towards a wall. The marbles will compete for the grooves on the slope, and come to rest at the lowest points. These points represent the eventual cell fates, that is, tissue types. A key theme in this work is that the final form of an organism does not develop entirely and exclusively from a blueprint specified in the genetic program, but rather is a result of the way the genes interact with the environment throughout the developmental process. (4-5)Waddington suggested that these concurrent interacting influences of genotype and environment could best be conceptualized as an epigenetic landscape, a domain of multiple hills and valleys; and that the growth and development of the organism could be likened to a marble making its way downhill. “Well-worn” or “beaten” paths pathways along which the course of development of an organism normally unfolds were termed chreodes. In the epigenetic landscape, chreodes are the developmental trajectories in the landscape and the epigenetic landscape itself represents the probability distribution of the developmental outcomes. In essence, the balls are much more likely to wind up at the base of a deeper valley, than stuck on some shelf or side valley. As the ball rolls down the landscape, it can be buffered by external or internal influences and perturbations; but it tends to return to the base valley, the chreode. (6,7) The resistance of phenotypic variations to environmental or genetic influences is calledcanalization. Another way of thinking about it: Canalization is a measure of the ability of a population to produce the same phenotype regardless of variability of its environment or genotype. In Waddington’s epigenetic landscape a canalized trait would be a valley enclosed by high ridges, safely guiding the phenotype to its “fate.” This phenotypic buffering of the developmental systems can produce a “wild-type” phenotype (or what might more accurately be called a phenotypic mean) in the face of various mutations or environmental insults.In many ways, canalization is the opposite of phenotype plasticity, since it works to insure that phenotypic variation is limited to the degrees that the same phenotype is produced regardless of genotypic or environmental changes. Traits that are highly canalized show little capacity for variation."
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שייך לקטגוריות 3. השפעת הסביבה = חוק | להשאיר תגובה | |