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Unlocking the Mysteries of ‘Genetic Drift’

October 26, 2016

Remember playing with the copy machine as a kid? You’d make one copy, copy that copy, and so on—until you ended up with a completely faded image. (Assuming you even had an image left at all.)

You’ll often hear among some cannabis breeders the so-called “genetic drift” myth. They’ll claim that if you keep taking clone cuts from certain strains, those clones will eventually degrade in quality—just like making copies of the copies. But that’s not really what genetic drift is.

The history of genetic drift

The true concept of genetic drift started in the 1920s. This was several decades after Charles Darwin had already revolutionized biology with his theory of evolution, but scientists still didn’t know how certain traits were passed on. We had some clues from Gregor Mendel’s pea studies, but Mendelian genetics and Darwinian evolution hadn’t been combined yet. In the ’20s, biologists recognized that certain genes and traits changed in a population without any adaptive or environmental pressures.

For example, let’s say there are two types of the same bird species on an island: some with silver feathers and some with gold feathers. The color of their feathers confers no special survival advantages, and the colors don’t harm the birds, either. So, these colors are “neutral mutations.” After studying these birds for several years, we notice that the ratio of silver-feathered birds to gold-feathered birds is changing. There used to be a ratio of 1 silver to 1 gold, but now it’s 10 silvers to 1 gold. Nothing happened on our island that should have selected one color of bird over the other. It just happened randomly; this is what is known as genetic drift.

Today, population geneticists refer to genetic drift as a “sampling error.” This is something that happens with real-world populations. No sampling is ever perfect, and that’s what we’re seeing with genetic drift. The sampling error happens over and over again, until it’s amplified and becomes the most prevalent (or, in some cases, the only) gene.

What’s genetic drift have to do with cloning? Probably nothing. Genetic drift applies only to populations of organisms that reproduce sexually. When we’re talking about cloning cannabis, we’re dealing with only one organism. Of course, we may produce thousands of copies of that individual plant, but it’s still only one plant. There’s (hopefully) no pollination going on, so genetic drift does not apply.

New clones, new traits

The question of why all of plant’s clones aren’t 100 percent the same isn’t easy to answer, mainly because we haven’t studied cannabis as much as we’d like, especially in large-scale grows. Most of the research was performed in labs on lower potency plants and small sample sizes. However, we have a ton of research on other plants.

It’s possible that clones are themselves producing new genes or deleting old ones. Back in 2011, a study from Oxford University showed that no clone was a perfect copy. Genetic analysis showed that when genes regenerated new tissue, they tended to spontaneously create new genes. It hasn’t been confirmed whether or not cannabis does this, but it’s possible.

The Oxford study called the phenomenon “regenerative mutation.” Some genes would be duplicated in the process, while other genes were deleted from the new clone altogether. However, this study looked at the thale cress plant. And as similar as regenerative mutation and genetic drift may seem, they’re still not the same thing.

Epigenetics and stress

Another reason we may see changes in some clones is stress. Stress doesn’t change the genetic makeup of a clone, but it can change how its genes are expressed through a process called epigenetics, a relatively new field of biology. Over the last few decades, we realized that DNA and genetic expression are not set in stone. The experiences of a parent can change the way their DNA is expressed, and they can pass those changes on to their offspring.

Epigenetics may explain why people who experience severe trauma (such as war) might beget children who are more prone to disease and mental illness. The stress changed the way the parents’ genes were expressed, and those changes were passed on to their children. Again, the DNA itself didn’t change, but little control mechanisms (such as chemicals) produced by the body changed whether those genes were turned on, off or set to overdrive.

What are these stress culprits in our cannabis plants? Sometimes a mother plant just gets old. Sometimes her feeding cycle is changed, or she gets sick or injured or both. Some growers suspect the heavy use of synthetic fertilizers or hormones may epigenetically alter their mothers, causing the clones to lose some desired trait.

When it comes to making clones, remember this: The act of cloning is a stressful act. You’re damaging tissue by severing part of the plant from itself. Clones also get transplanted and transported all over the place, which can also induce stress. Once this happens dozens, if not hundreds, of times to a series of clones, we may end up with different qualities in our clones than what we started with.

What can be done?

If clones lose their vigor over time, there’s really not much anyone can do. Some growers may be able to recover the missing traits from a mother plant, or by back-crossing a particular clone. But usually once a mother stops producing the desired traits in her clones, it’s probably time to pollinate her and let nature take its course.

Fortunately, most strains produce fairly stable clones. As long as you take extra good care of the mother plant, and you baby the clones, you should get pretty consistent results no matter how often you clone.


By Randy Robinson
Cannabis Cultivation Today articles are for informational purposes only and should not be considered legal guidance or advice on grow practices. You should contact an attorney or a qualified cultivation consultant for specific compliance and cultivation advice.
© 2016 CAN Performance Group, LLC. All rights reserved.



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