Dr. Peter J. D'Adamo
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."
| שייך לנושאים: 1-13 - חינוך אינטגרלי, -מקורות מדעיים, השפעת הסביבה, 3. השפעת הסביבה = חוק |
תגובות
להשאיר תגובה
יש להרשם כדי להוסיף תגובות.