Genetic memory (biology)
Encyclopedia
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.
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. Examples are methylation
patterns of the DNA molecule itself and proteins involved in packaging DNA, such as histone
s (also referred to as "histone code").
s. 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 vaccination
s. Antibody
genes in B and T lymphocyte
s 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 cell
s capable of producing these antibodies form the basis for acquired immunological memory. 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.
(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"). 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 Russia
n 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
).
, 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.
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. 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.
, genetic memory refers the inheritance of instinct
in animals and humans.
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, 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
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
or meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
), it is genetic.
Somatic 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 zygoteZygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
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
Epigenetics
In biology, and specifically genetics, epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence – hence the name epi- -genetics...
processes that affect DNA-protein interactions to record this cellular memory in the form of mitotically
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
stable changes of the genetic material without a change in the DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
sequence itself. This is typically achieved via changes of the chromatin
Chromatin
Chromatin is the combination of DNA and proteins that make up the contents of the nucleus of a cell. The primary functions of chromatin are; to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis and prevent DNA damage, and to control gene...
structure. Examples are methylation
Methylation
In the chemical sciences, methylation denotes the addition of a methyl group to a substrate or the substitution of an atom or group by a methyl group. Methylation is a form of alkylation with, to be specific, a methyl group, rather than a larger carbon chain, replacing a hydrogen atom...
patterns of the DNA molecule itself and proteins involved in packaging DNA, such as histone
Histone
In biology, histones are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes. They are the chief protein components of chromatin, acting as spools around which DNA winds, and play a role in gene regulation...
s (also referred to as "histone code").
In animals
A case of somatic genetic memory is the immunological memory of the adaptive immune response in vertebrateVertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s. 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 vaccination
Vaccination
Vaccination is the administration of antigenic material to stimulate the immune system of an individual to develop adaptive immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by many pathogens...
s. Antibody
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
genes in B and T lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s 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
Antigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
(e.g. following vaccination or an infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
with a pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
), these antibodies are further fine-tuned via hypermutation. Memory B cell
Memory B cell
Memory B cells are a B cell sub-type that are formed following primary infection.-Primary response, paratopes, and epitopes:In wake of first infection involving a particular antigen, the responding naïve cells proliferate to produce a colony of cells, most of which differentiate into the plasma...
s capable of producing these antibodies form the basis for acquired immunological memory. 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 vernalizationVernalization
Vernalization is the acquisition of a plant's ability to flower or germinate in the spring by exposure to the prolonged cold of winter...
(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
Chromatin remodeling
Chromatin remodeling is the enzyme-assisted movement of nucleosomes on DNA.This is performed by chromatin remodeling complexes like SWI/SNF , RSC and Imitation SWI complexes ....
which leads to mitotically stable changes in gene expression (the "winter code"). 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 Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n geneticist Trofim Lysenko
Trofim Lysenko
Trofim Denisovich Lysenko was a Soviet agronomist of Ukrainian origin, who was director of Soviet biology under Joseph Stalin. Lysenko rejected Mendelian genetics in favor of the hybridization theories of Russian horticulturist Ivan Vladimirovich Michurin, and adopted them into a powerful...
. 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
Lysenkoism
Lysenkoism, or Lysenko-Michurinism, also denotes the biological inheritance principle which Trofim Lysenko subscribed to and which derive from theories of the heritability of acquired characteristics, a body of biological inheritance theory which departs from Mendelism and that Lysenko named...
).
Inherited epigenetic memory
In geneticsGenetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
, 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
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
. In contrast, somatic genetic memories are passed on by mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
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.
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.Evolution
In population geneticsPopulation genetics
Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...
and evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
, 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
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
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. 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
Lamarckism
Lamarckism is the idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring . It is named after the French biologist Jean-Baptiste Lamarck , who incorporated the action of soft inheritance into his evolutionary theories...
to explain the inheritance of evolutionary changes.
Animal behavior
In ethologyEthology
Ethology is the scientific study of animal behavior, and a sub-topic of zoology....
, genetic memory refers the inheritance of instinct
Instinct
Instinct or innate behavior is the inherent inclination of a living organism toward a particular behavior.The simplest example of an instinctive behavior is a fixed action pattern, in which a very short to medium length sequence of actions, without variation, are carried out in response to a...
in animals and humans.