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In 1809, the French naturalist Jean Baptiste de Lamarck proposed the law of inheritance of acquired traits. According to her, the traits that are acquired in life would be transmittable to the following generations. For example, according to Lamarck, those giraffes that elongated their necks transmitted this trait to their descendants, which would explain the neck characteristics of modern giraffes.
From various studies, it is known that acquired traits are not encoded in an individual’s DNA, and therefore there is not enough scientific consensus to affirm that they can be transmitted to offspring during reproduction. For a trait to be passed on to the next generation, it must be in your DNA. Taking this into account, Lamarck’s theory was almost completely rejected after 1930.
Currently, an acquired trait is defined as a characteristic that produces a phenotype as a result of environmental influence . A phenotype is the expression of the genotype, that is, the traits that are observable (eye color, height, blood type, among others); The genotype constitutes the genes of an organism.
Despite the rejection of Lamarck’s theory, phenomena have been observed since the 1990s that apparently show what appears to be an inheritance of acquired traits. Studies have been carried out in this regard in organisms such as plants, worms and sperm from certain mammals.
Inheritance of acquired traits in plants
In 1962, in a study by the University College of Wales, it was observed that flax plants grown in nutrient-rich media exhibited a three times greater weight when compared to those grown in nutrient-poor media. This trait was passed down for six generations, regardless of the culture conditions employed thereafter. Seeing this, the researchers concluded that the induction of new traits can be passed on, depending on environmental conditions and the genetic makeup of the plants.
During the 1990s, other cases of inheritance of acquired traits were reported: dwarfism in rice, different maturation times in hybrids between wheat and rye, and early flowering in flax plants, were induced traits that were also stably transmitted in at least two generations.
However, the molecular basis for the inheritance of acquired traits is not fully known. It is believed that changes in gene expression are not induced by alteration of the nucleotide sequence, that is, they do not occur due to mutations. Instead, it is considered that the modification in the phenotypes occurs due to some other factors that respond reversibly to external stimuli.
Inheritance of acquired traits in animals
In 2011, a Columbia University Medical Center (CUMC) study experimented with roundworms that developed resistance to a virus and were able to pass that immunity on to their offspring for consecutive generations. This is direct evidence that an acquired trait can be inherited without DNA being involved.
In their study, the researchers considered that ribonucleic acid interference (RNAi) was involved in the inheritance of acquired traits. Normally, RNAi is involved in defense against viruses. When a virus infects a cell, RNAi breaks down messenger ribonucleic acid (mRNA) that is normally present in the cell and is compatible with the virus. In this way, the virus cannot reproduce.
RNAi production can be artificially promoted by delivering virus to healthy individuals. Immune activity resulting from this procedure is observed in treated animals and their offspring. The researchers concluded that the ability to fend off the virus is “memorized” in the form of viral RNA, which is then passed on to subsequent generations.
On the other hand, it is known that spermatozoa RNA can mediate the transmission of paternally acquired phenotypes, and those derived from mental stress and metabolic disorders induced by diet. However, it is still unknown how many types of acquired traits can be passed on to offspring via sperm, and under what circumstances this occurs.
In humans, some cases of inheritance of acquired traits have been reported. One that is frequently mentioned is that of malnourished pregnant Dutch mothers, whose children and grandchildren were found to be susceptible to both obesity and other metabolic disorders.
These findings are of interest to epigenetics, that is, the study of changes in gene function that are inherited and do not involve a change in the DNA sequence. Despite the controversies, it is convenient to re-evaluate the Lamarckian inheritance from the point of view of this discipline, taking into account the cited studies in plants, nematodes and mammalian sperm.
Sources
Columbia University Medical Center, CUMC. Howard Hughes Medical Institute. Acquired Traits Can Be Inherited via Small RNAs , 2011.
Chen, Q., Yan, W. & Duan, E. Epigenetic inheritance of acquired traits through sperm RNAs and sperm RNA modifications . Nat Rev Genet, 17, 733–743, 2016. https://doi.org/10.1038/nrg.2016.106
Sano H. Inheritance of acquired traits in plants: reinstatement of Lamarck . Plant signaling & behavior , 5(4), 346–348, 2010. https://doi.org/10.4161/psb.5.4.10803
