Mendel And Lysenko: Lies My Biology Teacher Told Me

http://www.the-scientist.com/?articles.view/articleNo/44628/title/Ghosts-in-the-Genome/

“Lysenko was committed to the idea that, within the space of a single generation, the environment could alter the phenotype of future generations, an idea that is now often (imprecisely) referred to as “Lamarckian” inheritance.

However, the scientific community has discovered over the past few decades that the idea that acquired characters can be inherited may not be completely off the mark. It turns out that epigenetic marks, information not encoded in the genome’s sequence, do respond to environmental conditions within an organism’s lifetime, and recent evidence suggests that such information may be inherited.

These findings have helped motivate modern research into the oft-discredited study of transgenerational effects of the environment. Researchers are now beginning to understand the mechanisms of epigenetic inheritance and to generate evidence for the idea that the experiences of an ancestral population can influence future generations.

Not only is epigenetic information inherited during cellular division, but it can also be passed from one generation to the next in multicellular organisms, a phenomenon known as transgenerational epigenetics. This requires that epigenetic information be carried in the gametes—sperm and eggs—and be maintained throughout the dramatic changes that occur during gamete production, fertilization, and early development. While researchers once considered this unlikely, recent studies have begun to demonstrate that parents can and do pass on epigenetic information to their children.

This idea, often referred to as the inheritance of acquired characters, was one aspect of Jean-Baptiste Lamarck’s early evolutionary theories. But the current use of “Lamarckian inheritance” to refer to transgenerational epigenetic inheritance is something of a misnomer. In fact, the inheritance of acquired characters was hardly the defining feature of Lamarck’s beliefs. His evolutionary theory did not include the basic concept of natural selection, and did not have a place for phenotypic variation existing prior to environmental challenges. Moreover, both Darwin and Lamarck believed that traits acquired in one’s lifetime could be passed on. Famously, Darwin even developed a model of inheritance that invoked “gemmules,” which carried information from all parts of the body to alter the characteristics of the next generation.

Today, a number of studies document a link between ancestral environmental conditions and changes in offspring behavior or metabolism, potentially validating some of the thinking of both seminal evolutionary theorists on this topic. It is now becoming clear that the environments of both the mother and the father can influence offspring phenotype.

But we now know that sperm carry epigenetic information in addition to their haploid genomic payload. Moreover, during mating, a male provides his partner with a bolus of seminal fluid, which carries proteins and other molecules that might have signaling roles. Fathers may also contribute microbes to their partner and offspring by direct contact or in feces. There is even evidence that in some species a mother’s investment in offspring is modulated by her judgment of the prospective father’s adequacy, so the impression a male makes on his mate has the potential to alter his offspring’s future. Given these contributions, we and others have used lab models to ask how paternal exposure history may influence offspring behavior, metabolism, or disease risk.6

Dias and Ressler found that the offspring of the fear-conditioned males had more neurons expressing the olfactory receptor specific for the shock-paired odor.10 This finding raises the exciting and surprising possibility that sperm can transmit thousands of bits of information to offspring. If odorants can induce specific responses in offspring, why not other factors such as hormones, and so forth? It will be very exciting to see whether other labs have similar results with effects on offspring of paternal exposure to odorants and other small molecules.

In other words, factors outside of the father’s diet can alter cholesterol metabolism to a far greater extent than paternal diet, even in genetically identical animals held in carefully controlled conditions. Other paternal effects are similarly subtle, presumably one of the reasons why paternal environmental effects have only been uncovered in the past decade or so. The next decade or two should be an exciting time as we learn more about what, how, and why we tell our children about the world around us before they’re even born. “

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