Genetic memory (biology)

In biology, memory is present if the state of a biological system depends on its 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 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.

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. Examples are methylation patterns of the DNA molecule itself and proteins involved in packaging DNA, such as histones (also referred to as "histone code").

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. 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.

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