I introduce genetics by engaging students in a discussion of eye color. Mendelian genetics and the basic laws of dominant and recessive traits transition to the inheritance of traits and disorders. There is always the inevitable question: If I inherit the gene that is related to alcoholism, is that my destiny? Why do some identical twins, naturally occurring clones of each other, differ in their health as they get older?
Epigenetics is the study of chemical reactions that occur during the development of an organism and activate or deactivate certain parts of the genome. Think of genetic switches that can be turned on or off during various stages of our lives. This relatively new focus hints at environmental influences on gene expression.
In this audio slide show, two genetically identical twin mice are compared. The left one is obese and prone to diabetes, whereas its twin on the right is lean and less likely to express diabetes. The cause is attributed to epigenome, which is being compared to a second genome within an organism.
The study of epigenetics is truly a breakthrough in the study of gene expression and the influence of environmental factors.