Wednesday, April 22, 2009

Could Offspring Inherit Acquired Traits?


A team of researchers lead by Larry Feig has recently found evidence suggesting that certain acquired traits could be passed down to offspring. If it is true, the implications for our understanding of genetics are notable.



Feig and his colleagues bred “knock-out” mice, which due to a genetic defect lack ras-GRF proteins, which play a key role in Long Term Potentiation. When placed in a shock chamber, knock-out mice are unable to associate the shock with the cage, and do not learn to fear the cage itself like normal mice. However, many experiments have shown that they can overcome this memory deficiency if they are exposed to an Enriched Environment as juveniles. This includes stimulatory objects, enhanced social interactions, and opportunities for exercise. Enriched Environments unlock a camp/p38-dependent signaling cascade that enhances Long Term Potentiation. Knock-out mice reared in an Enriched Environment respond to the shock chamber normally, contextualizing their fear and showing increased freezing responses whenever in the cage, not just after a shock.


Feig’s team wanted to know if the mice’s ability to overcome their genetic defect could be passed down to offspring. They bred mice lacking ras-GRF to test the theory. They found that the offspring of Enriched knock-out mice responded normally to the shock chamber, and had increased Long Term Potentiation. To assure the effect wasn’t environmental, the mice were raised by a foster mother in an un-enriched environment. These mice were still able to overcome their genetic deficiency, proving that the enhanced Long Term Potentiation wasn’t learned.


This effect was only seen over one generation (grandchildren did not also inherit the “rescued” memory) and was only carried by the mother. Enriched male knock-out mice did not produce offspring that could overcome their lack of ras-GRF without enrichment.


As of yet, Feig’s team does not know how this happens. No mechanism in our understanding of modern genetics allows for this.



If this effect is as it appears, and traits acquired in a mother’s life before conception are being passed on to offspring, the implications for the field of genetics are staggering. It contradicts what we currently know about genetic inheritance.



Our current understanding of genetics is based on the work of Gregor Mendel, a monk who studied pea traits in the 19th century. Through studying characteristics like flower color and seed shape, he was able to see that certain traits were dominant or recessive, (later learned to be expressed by genes) and they occur in pairs in organisms. However, when organisms reproduce, the genes split and unite, competing or combining to express a phenotype. Most work in this field is based upon Mendelian theories. Mendelian genetics provided the mechanism for Darwinian evolution, combining to create the contemporary theory of evolution, i.e. traits that are successful result in more offspring for the successful organism, leading to even more expression of the successful gene, leading to eventual adaptation and evolution. Only genes are expressed in an offspring. If a woman was burned by acid, her child will not be born with burns as well, because the burns were acquired in her life, they are not part of her DNA.



Before Mendel, our understanding of trait inheritance was based on a Naturalist named Jean-Baptiste Lamarck. He believed that adaptations in animals were based on acquired traits that were passed on to offspring. A giraffe, for example, would have started with a relatively short neck, but would stretch itself to reach a higher branch. When the giraffe had a baby, that giraffe would be born with its mother’s longer neck and would in turn stretch itself a little longer to reach even higher branches, giving birth to an offspring with an even longer neck. This process would continue until what we now know as a giraffe was born.


Feig’s findings suggest that genetics may have a Lamarckian component, with acquired traits able to overcome our model of genetic inheritance and express themselves in a first generation offspring. Given that the mechanism for this phenomenon is unknown, it is quite possible that there is a perfectly reasonable explanation for this occurrence, but there is a small possibility that genetic inheritance as we know it is flawed. Granted, I strongly believe that is NOT the case, but if it is, not only would the field of genetics have to be completely rethought, but also its dependent fields such as evolutionary biology and the study of genetic diseases would need a major overhaul.


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