ep·i·ge·net·ics
the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.
AGCT, adenine, guanine, cytosine, thymine, are the nucleotides that make up the four-letter alphabet of DNA. DNA is transcribed into RNA. From RNA, proteins are translated and the building blocks for life are created. A single cell contains all of the information to build an entire organism including leaves, stems, flowers, and roots. Cells differentiate into distinct types because particular genes are active in distinct cell types. Signaling causes this specialization to occur as epigenetic tags activate and silence the expression of specific genes.
The physical structure of the DNA determines if a gene can be expressed. If the DNA is tightly wrapped around histones and covered in chemical tags then the DNA will be unreadable. Signals from the outside world can cause the removal of the epigenetic tags allowing the DNA to relax and become readable.
Plants are exposed to stressors such as heat, predation, drought, cold, humidity, excess light, and infection. In each of these cases, these stressors trigger a cascade of signals that results in a response.
Scientists recently studied the chemical tags in European holly to determine if deer herbivory changed the genetic structure and genetic expression. The structure of the leaf can present in two forms, prickly or smooth. The scientists saw a decrease in chemical tags among the prickly leave phenotypes and also saw an increase in the prickly leave phenotypes when the holly was being munched on.
Increasingly interesting are the studies looking at how these epigenetic changes are passed through generations. Scientists studied this phenomenon in Arabidopsis by infecting the parent with a bacterial infection. The parent mustered defense mechanisms to combat the infection.
The response was found in the second generation even without the bacterial infection present to stimulate a response.
How is this related to cannabis?
We keep mothers as genetic reservoirs. Sometimes these mothers encounter stressors and when we flower out the clones they begin to show signs of degradation. This could be caused by the change in genetic expression as the plant responds to stress.
One of the most deleterious stress responses is the hermaphrodite trait in female plants. Undiscovered hermies can pollinate a flowering room leading to lower grade flowers considered undesirable by most smokers. Sometimes smokers flower out this bag seed and see that the progeny also presents with the hermaphrodite trait.
A hypothesis could be formed that the stress induced hermaphrodite response is primed in the next generation.
Some cannabis breeders choose not to breed with hermaphrodite progeny or create feminized seeds due to both the anecdotal evidence that this characteristic is expressed in subsequent generations and the peer-reviewed studies on other plant species pointing to the generational expression of stress responses. However, there is hope that breeding through multiple generational lines can erase the response and the genes coding for the stress response will become tightly wrapped around histones with tags yet again, preventing expression until they are exposed to stress.
This article was written by valkyrie_onhigh.
Sources:
http://onlinelibrary.wiley.com/doi/10.1111/boj.12007/abstract
http://www.plantphysiol.org/content/158/2/545.short
http://learn.genetics.utah.edu/content/epigenetics/
