Weismann barrier
Encyclopedia
The Weismann barrier is the principle that hereditary information moves only from genes to body cells, and never in reverse. In more precise terminology hereditary information moves only from germline
cells to somatic cells (that is, soma to germline feedback is impossible).
This does not refer to the central dogma of molecular biology
which states that no sequential information can travel from protein
to DNA
or RNA
.
The Weismann barrier is very important as it has implications for human gene therapy
. If the Weismann barrier is permeable, then genetic treatments of somatic cells may actually result in a heritable change to the genome, possibly resulting in the genetic engineering
of the human species rather than just individuals. It also has implications in our understanding of evolution
as it would imply that species aren't nearly as separable genetically as we once thought. Furthermore it would open the door to the existence of certain Lamarckian
concepts that previously had no supporting mechanism.
The use of this theory is sometimes referred to as Weismannism.
was an early step in the founding of the science of genetics
, and like any part of any science is subject to review in light of new data. Although the principle was seriously questioned at times in the 20th century, the research of Paul Kammerer
and Trofim Lysenko
failed to weaken the principle among the greater scientific community.
.
Evidence has begun to mount for horizontal gene transfer
. Different species appear to be swapping genes through the activities of retrovirus
es. Retro-viruses are able to transfer genes between species because they reproduce by integrating their code into the genome of the host and they often move nearby code in the infected cell as well. Seeing as these viruses use RNA as their genetic information they need to use reverse transcriptase to convert their code into DNA first. If the cell they infect is a germline cell then that integrated DNA can become part of the gene pool
of that species.
Other evidence against Weismann's barrier is found in the immune system
. A controversial theory of Edward J. Steele
's suggests that endogenous retrovirus
es carry new versions of V genes from soma cells in the immune system to the germ line cells. This theory is expounded in his book Lamarck's signature. Steele observes that the immune system needs to be able to evolve fast to match the evolutionary pressure (as the infective agents evolve very fast). He also observes that there are plenty of endogenous retro-viruses in our genome and it seems likely that they have some purpose.
Even if both of these possible exceptions turn out to be legitimate, the Weismann barrier just loses its absolute status. Without further examples, the penetration of the Weismann barrier is still very much an exception.
Germline
In biology and genetics, the germline of a mature or developing individual is the line of germ cells that have genetic material that may be passed to a child.For example, gametes such as the sperm or the egg, are part of the germline...
cells to somatic cells (that is, soma to germline feedback is impossible).
This does not refer to the central dogma of molecular biology
Central dogma of molecular biology
The central dogma of molecular biology was first articulated by Francis Crick in 1958 and re-stated in a Nature paper published in 1970:In other words, the process of producing proteins is irreversible: a protein cannot be used to create DNA....
which states that no sequential information can travel from protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
to 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...
or RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
.
The Weismann barrier is very important as it has implications for human gene therapy
Gene therapy
Gene therapy is the insertion, alteration, or removal of genes within an individual's cells and biological tissues to treat disease. It is a technique for correcting defective genes that are responsible for disease development...
. If the Weismann barrier is permeable, then genetic treatments of somatic cells may actually result in a heritable change to the genome, possibly resulting in the genetic engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...
of the human species rather than just individuals. It also has implications in our understanding of 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...
as it would imply that species aren't nearly as separable genetically as we once thought. Furthermore it would open the door to the existence of certain Lamarckian
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...
concepts that previously had no supporting mechanism.
The use of this theory is sometimes referred to as Weismannism.
History
The work of 19th century biologist August WeismannAugust Weismann
Friedrich Leopold August Weismann was a German evolutionary biologist. Ernst Mayr ranked him the second most notable evolutionary theorist of the 19th century, after Charles Darwin...
was an early step in the founding of the science of genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
, and like any part of any science is subject to review in light of new data. Although the principle was seriously questioned at times in the 20th century, the research of Paul Kammerer
Paul Kammerer
Paul Kammerer was an Austrian biologist who studied and advocated the now abandoned Lamarckian theory of inheritance – the notion that organisms may pass to their offspring characteristics they have acquired in their lifetime...
and 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...
failed to weaken the principle among the greater scientific community.
Recent criticism
In the late 20th century there have been criticisms of an impermeable Weismann barrier. These criticisms are all centered around the activities of an enzyme called reverse transcriptaseReverse transcriptase
In the fields of molecular biology and biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into single-stranded DNA. It also helps in the formation of a double helix DNA once the RNA has been reverse...
.
Evidence has begun to mount for horizontal gene transfer
Horizontal gene transfer
Horizontal gene transfer , also lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism...
. Different species appear to be swapping genes through the activities of retrovirus
Retrovirus
A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA...
es. Retro-viruses are able to transfer genes between species because they reproduce by integrating their code into the genome of the host and they often move nearby code in the infected cell as well. Seeing as these viruses use RNA as their genetic information they need to use reverse transcriptase to convert their code into DNA first. If the cell they infect is a germline cell then that integrated DNA can become part of the gene pool
Gene pool
In population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...
of that species.
Other evidence against Weismann's barrier is found in the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
. A controversial theory of Edward J. Steele
Edward J. Steele
Edward J. Steele is an Australian molecular immunologist formerly with the University of Wollongong, now listed as a visiting fellow at the Murdoch University. Steele's research has led a resurgent interest in the French scientist Jean-Baptiste de Lamarck, the man who developed the first theory of...
's suggests that endogenous retrovirus
Endogenous retrovirus
Endogenous retroviruses are sequences in the genome thought to be derived from ancient viral infections of germ cells in humans, mammals and other vertebrates; as such their proviruses are passed on to the next generation and now remain in the genome....
es carry new versions of V genes from soma cells in the immune system to the germ line cells. This theory is expounded in his book Lamarck's signature. Steele observes that the immune system needs to be able to evolve fast to match the evolutionary pressure (as the infective agents evolve very fast). He also observes that there are plenty of endogenous retro-viruses in our genome and it seems likely that they have some purpose.
Even if both of these possible exceptions turn out to be legitimate, the Weismann barrier just loses its absolute status. Without further examples, the penetration of the Weismann barrier is still very much an exception.