What is the epigenome and epigenetic inheritance?
The epigenome is the second layer of structure, the chemical tags covering DNA and the histones. It’s more flexible than DNA, reacting to signals from the outside environment. It tightly wraps inactive (recessive) genes, making them unreadable, while it makes active genes more accessible. External factors in the environment can have different outcomes on the epigenome. For example, cancer activates different genes that have different outcomes, such as cell growth. The original concept around passing down traits to future generations was that inheritance happens only through the DNA code that passes from parents to offspring. However, recent finds show that there is more to the story than just this. Epigenetic inheritance is when a parent’s experiences can be passed down to future generations, if the form of epigenetic chemical tags.
Does this even happen in real life?
Yes! There are multiple examples of epigenetic inheritance in nature such as toad flax, wild radish, and water fleas.
The difference between common and peloric is the shape of their flowers (pictured on the left), due to a difference in one gene in the epigenetic tag. Peloric toad flax pass this on to future generations.
Wild radish plants all look the same, unlike toad flax. However, they have a special defense against caterpillars, which are their predators. They produce distasteful chemicals and grow protective spines. However, a lot of plants do this as a defense. What is interesting about this plant is that it's offspring also have these defenses, even in a caterpillar free environment.
Similar to the wild radish, female water fleas respond to chemical signals from their predators by growing protective helmets. This continues for two generations (down to the grandchildren) even if they grow in environments without predators.
The Queen Bee:
Epigenetic tags turn off certain genes in response to environmental factors. This is visible in bees. Royal jelly is a protein rich substance from glands of worker bees, fed to the destined queen bee. This royal jelly silences Dnmt3, turning off the enzyme that silences queen genes. Due to this royal jelly diet, the queen bee will develop ovaries and other queenly behaviors, such as killing rival queens.
Anxiety in Lab Rats:
A real example of environmental factors affecting survival is in lab rats. It’s proven that maternal car, such as licking, grooming, and nursing, decreases anxiety levels in pups, compared to mother rats that ignore their pups. High anxiety levels in low nurtured rats are an advantage in environments where food is scare and danger is high. Low nurtured rats would be more likely to keep a low profile and respond quickly to stress. I don’t think this is the for human society as we live in a relatively low danger, nutrient rich environment. We wouldn’t have to worry about where our next meal is coming from or being in a high social standing.
How did we prove this in humans?
Proving epigenetics in humans is challenging because we have longer life spans and greater genetic diversity than other mammals. This makes it harder because it’s too time consuming to track multiple generations, and it becomes hard to rule out all genetic differences. However, it can represent snapshots of an environment in past and future environments, and how the epigenome reacted to it.
Nature vs Nurture:
One real life of epigenetics is the study of it in identical twins. It’s been discovered that although born with the same DNA, they become increasingly different over time. Some environmental factors that change the genome are diet, physical activity, exposure to toxins, and stress. If one twin gets a disease, researchers look for differences in the environment; when both twins get a disease, similarities in genes are compared. Some diseases with a strong connection to environmental factors are arthritis, stroke, cancer, and sclerosis. On the other hand, reading disabilities and autism have more genetic influence.
Thank you so much for reading! If you have any questions please upload them to the forum!
Sources: