Genetic memory

Genetic memory describes a variety of processes in biology and psychology by which genetic material confers a memory of an individual's or species' past history. It can refer to the genetic code of DNA, epigenetic changes to the genetic material, the inheritance of instinct, or racial memory in psychology. The term is also used for a method of computer prediction.

Biology

In biology, memory is present if the state of a biological system depends on its past history in addition to present conditions. If this memory is recorded in the genetic material and stably inherited through cell division (mitosis or meiosis), it is genetic.

Molecular biology

In molecular biology, genetic memory resides in the genetic material of the cell and is expressed via the genetic code used to translate it into proteins.cite journal |author=Nirenberg M |title=Genetic memory |journal=JAMA |volume=206 |issue=9 |pages=1973–7 |year=1968 |pmid=4880506 |doi=] Marshall Nirenberg (1968): "The genetic code". [http://nobelprize.org/nobel_prizes/medicine/laureates/1968/nirenberg-lecture.pdf Nobel Lecture] ] The genetic code enables cells to decode the information needed to construct the protein molecules that make up living cells and therefore record and store a one-dimensional blueprint for all the parts that make up an organism. This blueprint or genetic memory in the form of species-specific collections of genes (genotype or genome) is passed from cell to cell and from generation to generation in the form of DNA molecules. DNA therefore functions as a template for protein synthesis. Genetic memory can be modified by "epigenetic memory", a process by which changes in gene expression are passed on through mitosis or meiosis through factors other than DNA sequence.

omatic memory

"Somatic memory" is limited to the organism and not passed on to subsequent generations. However, its mechanism may involve mitotically stable genetic memory. The term applies for cellular memory, animals' memory, and plants' memory, as described in the following paragraphs.

Cellular memory

All cells in multicellular organisms are derived from a pluripotent zygote and contain the same genetic material (with a few exceptions). However, they are capable of recording a history of their development within the organism leading to their specialized functions and limitations. Cells often employ epigenetic processes that affect DNA-protein interactions to record this "cellular memory" in the form of mitotically stable changes of the genetic material without a change in the DNA sequence itself. This is typically achieved via changes of the chromatin structure.cite journal |author=Hirose S |title=Crucial roles for chromatin dynamics in cellular memory |journal=J. Biochem. |volume=141 |issue=5 |pages=615–9 |year=2007 |pmid=17416595 |doi=10.1093/jb/mvm092] Examples are methylation patterns of the DNA molecule itself and proteins involved in packaging DNA, such as histones (also referred to as "histone code").cite journal |author=Bird A |title=DNA methylation patterns and epigenetic memory |journal=Genes Dev. |volume=16 |issue=1 |pages=6–21 |year=2002 |pmid=11782440 |doi=10.1101/gad.947102] cite journal |author=Turner BM |title=Cellular memory and the histone code |journal=Cell |volume=111 |issue=3 |pages=285–91 |year=2002 |pmid=12419240 |doi=]

In animals

A case of somatic genetic memory is the "immunological memory" of the adaptive immune response in vertebrates. The immune system is capable of learning to recognize pathogens and keeping a memory of this learning process, which is the basis of the success of vaccinations. Antibody genes in B and T lymphocytes are assembled from separate gene segments, giving each lymphocyte a unique antibody coding sequence leading to the vast diversity of antibodies in the immune system. If stimulated by an antigen (e.g. following vaccination or an infection with a pathogen), these antibodies are further fine-tuned via hypermutation. Memory B cells capable of producing these antibodies form the basis for acquired immunological memory.cite journal |author=Crotty S, Ahmed R |title=Immunological memory in humans |journal=Semin. Immunol. |volume=16 |issue=3 |pages=197–203 |year=2004 |pmid=15130504 |doi=10.1016/j.smim.2004.02.008] Each individual therefore carries a unique genetic memory of its immune system's close encounters with pathogens. As a somatic memory, this is not passed on to the next generation.

In plants

Plants that undergo vernalization (promotion of flowering by a prolonged exposure to cold temperatures) record a "genetic memory of winter" to gain the competence to flower. The process involves epigenetically recording the length of cold exposure through chromatin remodeling which leads to mitotically stable changes in gene expression (the "winter code").cite journal |author=Sung S, Amasino RM |title=Molecular genetic studies of the memory of winter |journal=J. Exp. Bot. |volume=57 |issue=13 |pages=3369–77 |year=2006 |pmid=16980591 |doi=10.1093/jxb/erl105] This releases the inhibition of flowering initiation and allows the plants to bloom with the correct timing at the onset of spring. As a somatic memory, this state is not passed on to subsequent generations but has to be acquired by each individual plant. The process of vernalization was falsely assumed to be a stably inherited genetic memory passed on to subsequent generations by the Russian geneticist Trofim Lysenko. Lysenko's claims of genetic memory and efforts to obtain or fabricate results in proof of it had disastrous effects for Russian genetics in the early 20th century (also see: Lysenkoism).cite journal |author=Amasino R |title=Vernalization, competence, and the epigenetic memory of winter |journal=Plant Cell |volume=16 |issue=10 |pages=2553–9 |year=2004 |pmid=15466409 |doi=10.1105/tpc.104.161070]

Inherited epigenetic memory

In genetics, genomic imprinting or other patterns of inheritance that are not determined by DNA sequence alone can form an epigenetic memory that is passed on to subsequent generations through meiosis. In contrast, somatic genetic memories are passed on by mitosis and limited to the individual, but are not passed on to the offspring. Both processes include similar epigenetic mechanisms, e.g. involving histones and methylation patterns.cite journal |author=Ooi SL, Henikoff S |title=Germline histone dynamics and epigenetics |journal=Curr. Opin. Cell Biol. |volume=19 |issue=3 |pages=257–65 |year=2007 |pmid=17467256 |doi=10.1016/j.ceb.2007.04.015] cite journal |author=Gehring M, Henikoff S |title=DNA methylation dynamics in plant genomes |journal=Biochim. Biophys. Acta |volume=1769 |issue=5-6 |pages=276–86 |year=2007 |pmid=17341434 |doi=10.1016/j.bbaexp.2007.01.009]

Microbial memory

In microbes, genetic memory is present in the form of inversion of specific DNA sequences serving as a switch between alternative patterns of gene expression.cite journal |author=Casadesús J, D'Ari R |title=Memory in bacteria and phage |journal=Bioessays |volume=24 |issue=6 |pages=512–8 |year=2002 |pmid=12111734 |doi=10.1002/bies.10102]

Evolution

In population genetics and evolution, genetic memory represents the recorded history of adaptive changes in a species. Selection of organisms carrying genes coding for the best adapted proteins results in the evolution of species. An example for such a genetic memory is the innate immune response that represents a recording of the history of common microbial and viral pathogens encountered throughout the evolutionary history of the species.cite journal |author=Dempsey PW, Vaidya SA, Cheng G |title=The art of war: Innate and adaptive immune responses |journal=Cell. Mol. Life Sci. |volume=60 |issue=12 |pages=2604–21 |year=2003 |pmid=14685686 |doi=10.1007/s00018-003-3180-y] In contrast to the somatic memory of the adaptive immune response, the innate immune response is present at birth and does not require the immune system to learn to recognize antigens.

In the history of theories of evolution, the proposed genetic memory of an individual's experiences and environmental influences was a central part of Lamarckism to explain the inheritance of evolutionary changes.

Animal behavior

In ethology, genetic memory refers the inheritance of instinct in animals and humans.

Psychology

In psychology, genetic memory is a memory present at birth that exists in the absence of sensory experience, and is incorporated into the genome over long spans of time.cite book|title=I of the Vortex: From Neurons to Self|author=Rodolfo R. Llinas|pages=190–191|date=2001|publisher=MIT Press|id=ISBN 0262621630] . It is based on the idea that common experiences of a species become incorporated into its genetic code, not by a Lamarckian process that encodes specific memories but by a much vaguer tendency to encode a readiness to respond in certain ways to certain stimuli. It is invoked to explain the racial memory postulated by Carl Jung, and differentiated from cultural memory, which is the retention of habits, customs, myths, and artifacts of social groups. [cite book|title=Mind And Its Evolution: A Dual Coding Theoretical Approach|author=Allan Paivio|pages=240|date=2006|publisher=Routledge|id=ISBN 0805852603] The latter postdates genetic memory in the evolution of the human species, only coming into being with the development of language, and thus the possibility of the transmission of experience. [cite book|title=The Civilization of Illiteracy|author=Mihai Nadin|pages=103–104|date=1997|publisher=Dresden University Press|id=ISBN 3931828387]

Genetic memory and language

Language, in the modern view, is considered to be only a partial product of genetic memory. The fact that humans can have languages is a property of the nervous system that is present at birth, and thus phylogenetic in character. However, perception of the particular set of phonemes specific to a native language only develops during ontogeny. There is no genetic predisposition towards the phonemic makeup of any single language. Children in a particular country are not genetically predisposed to speak the languages of that country, adding further weight to the assertion that genetic memory is not Lamarckian.

Historical views

In contrast to the modern view, in the 19th century biologists considered genetic memory to be a fusion of memory and heredity, and held it to be a Lamarckian mechanism. Ribot in 1881, for example, held that psychological and genetic memory were based upon a common mechanism, and that the former only differed from the latter in that it interacted with consciousness. [cite book|title=Steven's Handbook of Experimental Psychology|editor=Harold E. Pashler|chapter=Learning Mutants|page=201|author=Louis D. Matzel|date=2002|publisher=John Wiley and Sons|id=ISBN 0471650161] Hering and Semon developed general theories of memory, the latter inventing the idea of the engram and concomitant processes of "engraphy" and "ecphory". Semon divided memory into genetic memory and central nervous memory. [cite book|title=Functional Osteology and Myology of the Shoulder in the Chiroptera|author=Timothy L. Strickler|pages=325|date=1978|publisher=Karger Publishers|id=ISBN 3805526458]

This 19th century view is not wholly dead, albeit that it stands in stark contrast to the ideas of neo-Darwinism. Stuart Newman and Gerd B. Müller have contributed to the idea in the 21st century. [cite book|title=Environment, Development, and Evolution: Toward a Synthesis|author=Brian Keith Hall, Roy Douglas Pearson, and Gerd B. Müller|pages=17|date=2003|publisher=MIT Press|id=ISBN 0262083191]

Parapsychology

Some parapsychologists have postulated that specific experience is encoded in genes, and proposed this as an explanation for past life regression. However, parapsychologists generally dismiss this, on grounds that in those cases where past life regression has been considered, the subjects have no genetic link with the people whose lives they are considered to have regressed to; and that the idea is unsound as a mechanism for explaining how events could be recalled from past lives of people at points in those lives "after" they had had children. Parapsychologists generally agree with the biological view that genetic traits are dispositional — i.e that they merely encode a disposition to react in certain ways to environmental stimuli, and not actual memory or experience. [cite book|title=Death and Personal Survival: The Evidence for Life After Death|author=Robert F. Almeder|pages=28–29|date=1992|publisher=Rowman & Littlefield|id=ISBN 0822630168] [cite book|title=The Meme Machine|author=Susan J. Blackmore|pages=60|date=1999|publisher=Oxford University Press|id=ISBN 019286212X] [cite book|title=Language, Metaphysics, and Death|author=John Donnelly|pages=356|date=1994|publisher=Fordham Univ Press|id=ISBN 0823215628]

Computer science

In computer science, genetic memory refers to an artificial neural network combination of genetic algorithm and the mathematical model of sparse distributed memory. It can be used to predict weather patterns.cite book |author=Rogers, David (ed. Touretzky, David S.) |title=Advances in neural information processing systems: Weather prediction using a genetic memory |publisher=M. Kaufmann Publishers |location=Los Altos, Calif |year=1989 |pages=455-464 |isbn=1-55860-100-7 |oclc= |doi=] Genetic memory and genetic algorithms have also gained an interest in the creation of artificial life.cite journal |author=Rocha LM, Hordijk W |title=Material representations: From the genetic code to the evolution of cellular automata |journal=Artificial Life |volume=11 |issue= |pages=189–214 |year=2005 |pmid= |doi= ]

ee also

Genetic memory in fiction

References

Further reading

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* — Note that the definition talks of "information based upon" learning and experience, rather than about learning and experience themselves.