In the Argument section on page 159, Shenk argues that another biological factor plays a role in heredity besides DNA: epigenetics. While studying 2 types of the toadflax plant, scientists realized that the DNA of both plants was identical; the reason for their different appearances was their histones and chromatin-the packaging that surrounded the genes. It was later discovered that epigenetic changes can be inherited, just like genes. The packaging of DNA can alter appearance, such as the fur color of mice (Shenk 159), and even increase risks of diseases such as colon cancer (Shenk 160). In other words, the environment we live in presently and the influences we expose ourselves to can affect not only our own gene expression, but our descendants' gene expression as well.
We have learned that histones and chromatin play a role in gene transcription and expression. How might environmental influences physically change an organism's histones to regulate the expression of a certain gene? (see Chapter 18 in Campbell p.356-358). What implications does the malleability of our epigenomes have on our lifestyles, from what we eat, to the chemicals we use, to how we study? Do you think there are any limitations on the kinds of traits that your epigenome can influence?
Akila Khan (starlight608@gmail.com)
The numerous recent discoveries in the epigenome pose very interesting and important considerations for not only biologists, but anyone that decides to become a parent. As we learning in biology, gene expression is in part regulated by DNA methylation and Histone acetylation. Unacetylated chromatin consists of a tightly wrapped DNA-Histone complex that does not allow transcription to take place, effectively controlling gene expression on the basis of acetylation (Campbell 357). DNA methylation has a similar effect - methylating enzymes often present during cell differentiation in the embyro controls the long term inactivation of genes by adding a methyl group to the DNA base-pair itself (Campbell 358).
ReplyDeleteWhile biologists have been aware of these types of changes, it was a very recent discovery that these epigenetic changes can actually be passed on through epigenetic inheritance. Shenk does not put this implication lightly: he argues that this may be “the most important discovery in the science of heredity since the gene.” If Shenk argues that the true basis for human traits is GxE, genetics and environment playing off of each other, this exponentially expands the picture, bringing in influence from the environments of previous generations on the genetics of each new generation. Genetics and environment became even more inextricably intertwined with epigenetic inheritance.
Large scale studies, such as the Overkalix study in northern Sweden, have demonstrated the far reaching effects of epigenetics. Researchers analyzing birth record data in conjunction with harvest records showed that whether a child’s parent lived during a famine period or an abundance period affected the future life expectancy (http://www.bbc.co.uk/sn/tvradio/programmes/horizon/ghostgenes.shtml). Other experiments showed that traits such as stress levels can also be passed down in this manner, as well as predisposition to drug addiction, smoking, and other health factors.
For parents, this information is critical. They cannot simply write off their own unhealthy lifestyles, as their bad decisions have the potential to affect their children, and their children’s children. Parents have a responsibility to ensure the health of their children, and due to epigenetic inheritance, this applies well before the child is conceived. The relatively new field of epigenetics still has many discoveries to be made, and it is likely it show just how complex human gene expression is.
David Whisler (dwhis428@gmail.com)