In the second part of our blog series on plant breeding, we zoom in on DNA, the genetic code contained in every cell of all living plants. DNA is the key that unlocks all plant traits. Whenever breeders aim to develop better, stronger plants, they select the best DNA for crossbreeding, creating a new generation that carries the desirable traits this DNA represents.
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Plant Breeding And DNA
Plant breeding is a respectable profession carried out by specialists, but its basic principles are fairly easy to understand. Plant breeding revolves around the selection of specific traits. These traits are genetic traits they are encoded in the DNA stored in every cell of each living plant.
In essence, DNA is a biochemical code: a kind of recipe used by cells to produce certain proteins. These proteins allow the organism (i.e., the plant) to grow, to change colour or shape, to protect itself from disease, or to produce more fruits and flowers. The essence of plant breeding, therefore, is selecting the DNA of an outstanding plant, and then reproducing it to ensure that both the DNA and the outstanding traits it represents return in the next generation of plants.
DNA, or desoxyribonucleic acid, is a molecule of an exceptional length. You can find DNA in the nucleus of every cell of all plant and animal species. Basically, DNA molecules are like cookbooks containing thousands of recipes, each written using four ‘letters’: A, T, C, and G. Of course, these are not actual letters, but four different chemical structures called nucleotides. These four nucleotides are adenine (A), thymine (T), cytosine (C), and guanine (G).
A DNA molecule looks like a twin spiral, also know as a double helix. You will recognise the shape of DNA in the Amsterdam Genetics logo, blended with the triple crosses of the Amsterdam city emblem. That makes perfect sense, because we have grown famous by the cannabis seeds we have developed. That development is all about decades of careful plant breeding using the finest DNA in existence.
The Evolution Of DNA
DNA molecules are found in the core of the cells of every plant. There other forms of DNA that reside in less central parts of plant cells, too, such as mitochondrial DNA and certain particles in the cell’s plasma. We will not go into these types of DNA here, however, since that would needlessly complicate matters.
Most of the time, the long-winded, outstretched molecules of DNA’s double helix structure reside in the cell’s nucleus in a compact, rolled-up form. We call this contracted, robust form of DNA molecules ‘chromosomes’. The only moment when these chromosomes ‘stretch out’ into the winding strings of DNA is during cell division, which science usually refers to as mitosis.
After chromosomes unfold into double DNA helices, their code of ATCG molecules can be copied. This simple fact is key to understanding the secret of the evolution of all life on earth. During mitosis, cells are able to replicate and split into two new cells, each carrying inside the exact DNA of the original cell. To do so, the cell unwinds its DNA string, after which the entire molecule splits open like a microscopic zipper.
These two halves expose their parts of the genetic ATCG code to a ‘copier molecule’ called messenger RNA, which is similar in structure to DNA. Each A locks onto a T, while every C connects with a G, and vice versa. This results in two identical copies of what used to be one double helix; each with the exact identical DNA cookbook full of recipes on board. That means both new cells will display the same traits displayed by the original cell. This process is known as heredity. It is the basis of modern genetics, a sub-discipline of biology that constitutes the scientific foundation of plant breeding.
Heredity is a continuous process seen in all living organisms. It is how plants and animals replace old, dead cells by new copies. It is also how your cannabis plant (or your cactus or cat) grows: by turning one cell into two new cells the organism increases in size, from the very first cells originating from conception down to the gigantic clumps of cells that make up a giant sequoia tree or blue whale.
Cell division heredity also explain why you resemble your parents, and why people who live in the same part of the world for a long time are more like each other. Moreover, it account for the principles that underpin plant breeding, and therefore also why you get to order cannabis seeds that grow into the carefully bred strains you like to grow.
Reproduction And Copying DNA
Alright. So now we know that every cell of a plant contains the same DNA; and that these DNA cookbooks can copy themselves to create new cells. You may wonder at this point how this mechanism is so essential to plant breeding.
Well, in fact, there is one crucial aspect that we have not mentioned so far. In addition to the mitosis process described above, there is another type of cell division called meiosis. In the case of mitosis, the DNA contained in the chromosomes splits in half, too, but after that, the process changes. The cells divides itself into two reproductive cells, each carrying only half of the original double helix DNA in its nucleus.
These ‘half DNA cells’ are capable of merging with the reproductive cells of other plants. In the case of cannabis plants, male pollen cells can merge with reproductive cells found in the flowers of female plants. This happens during pollination: something that growers usually try to prevent at all costs, while breeders actively promote it as an essential step in creating new crossbreeds!
When two different reproductive cells merge together, something extraordinary happens. A new cell is formed, containing a spontaneous combination of bits of DNA from both the mother and father plants. This is a bit like throwing lots and lots of dice: the number of possible outcomes is astronomical because there are so many different genes available to form new combinations.
These new DNA combinations determine the genetic content of the seeds formed by pollinated mother plants (and which growers usually don’t want to find in their harvest). Once mitosis is complete, the parent plants have successfully managed to reproduce.
This new and wholly unique DNA code forms the basis for a new individual: the seed representing the next generation as the ‘baby’ or offspring of its parent plants. If that seed manages to germinate and grow up to become a new plant, it will display traits inherited from both parents. It has no choice in the matter; after all, every single cell of this new organism contains the same mix of genetic recipes provided by the mother and father plants. The predictability of this outcome is what breeders use to their advantage in plant breeding.
How Breeders Guide Plant Evolution
After this in-depth explanation of how DNA, cell division, and heredity work, we finally arrive in the domain of actual plant breeding. The following applies equally to breeding tomato plants, apple trees, or cannabis. Breeders of all plant species use the same insights into genetics to guide the evolution of the apple, tomato, or cannabis varieties they work with.
Out in the wild, among landrace populations, evolution is powered by reproduction and spontaneous DNA mutations (due to random changes or copying errors). Sometimes, recipes from the genetic cookbook are copied with a few mistakes. Most of the time, these copying errors change nothing: these mutations happen all the time in all organisms, consisting of billions of cells that keep on dividing. With so much copying going on, mistakes are bound to happen. In most of these cases, the error has no effect: nothing changes for the cell or the organism.
However, on very rare occasions, these copying errors do produce new DNA combinations that do change the cell. Usually, such mutated cells need to replicate many times over before they can have an effect on the organism (the plant) as a whole. Such effects generally tend to have negative consequences, such as disease, flawed metabolism, or structural problems like misshapen leaves.
Genius Genetics: Spontaneous Mutation
In certain exceptional cases, however, these spontaneous mutations happen to be improvements –random strokes of genetic genius. This occurs when the new trait offers the individual some kind of advantage over the ‘normal’ specimens of its generation. Suppose your cannabis seeds contains some spontaneously mutated DNA, turning it into a plant that is twice as resistant to bud rot as all other plants of that strain. There is a real chance that your plant and its buds will survive the mould infection, while the ‘normal’ plants don’t produce any useful harvest at all. The question is: would you throw this one plant away because apparently, it contains mutated DNA?
No, of course you wouldn’t. This is in fact the exact same decision that plant breeders try to make. Whenever the notice an exceptionally beautiful, large, strong, or tasty (i.e., ‘good’) specimen, they select that plant for crossbreeding into a new generation of plants that inherit the spontaneous mutation. This is how plant breeding can create new strains, such as the one with better resistance against bud rot in the example above.
Cannabis DNA And Plant Breeding
The evolution of every landrace of all plant species, and indeed, of all natural life, is based on these spontaneous mutations. Every new generation produces some mutants that differ from the normal specimens. Most of the time, they go unnoticed; other mutants are weaker, and some even die because of their mutations. Sometimes, though, these random mutations offer distinct advantages that improve a specimen’s chances of survival and reproduction compared to other individuals.
This usually occurs when the evolutionary pressure or selection pressure in the environment shifts, for instance when climate conditions change, or when a new predator or disease enters the scene. Suddenly, the existing genetics are no longer ideal; and so the mutants get their chance to shine. This is the famous (and often misunderstood) principle of ‘survival of the fittest’: the individuals that are best suited to deal with the new circumstances have the best chances to survive and reproduce, thus passing on their DNA to the next generation.
When this happens, the chances of seeing the advantageous mutation return in more specimens of the next generation increases. If the new situation persists, this ‘mutant offspring’ then has better chances of spreading their DNA to the next generation in turn, and so on. This is how new traits spread across populations.
This is how Charles Darwin’s important principle of natural selection works: the environment randomly ‘selects’ which specimens are best suited to survive. The fittest individuals tend to survive and pass on their DNA to following generations.
Natural Selection, Or Breeder’s Direction?
Now, don’t make the mistake of thinking that there is some kind of ‘plan’ behind this mighty evolutionary mechanism. And don’t think that ‘fitness’ is anything like what you do at the gym. Whoever is fittest, and therefore has better chances of survival, is determined in retrospect by the brute force to which they are exposed by the environment. There is no-one who ‘decided’ that cows with horns have better chances of survival than cows without. These horns are simply the outcome of a long sequence of random mutations, each of which happened to extend some minor advantage over the all other cows.
Ultimately, evolutionary pressure In the environment determines whether mutations ‘work’ or not, and whether they will return in future generations.
Beyond that, the randomness and whimsical spontaneity of natural selection is, unscientifically stated, quite a messy affair without any ‘intentional’ purpose to guide it. Sexual reproduction is very much like rolling the dice and hoping for the best.
This messy process does come with a number of advantages, though – otherwise, evolution probably wouldn’t have been the success story it appears to be. It leads to ever-greater diversity within species, as well as giving rise to new species with their own strong traits to help them survive in their specific habitats. Whenever new diseases come into play, there is a pretty good chance that some individuals happen to be resilient due to some random mutation that seemed useless up to that point.
Plant Breeding And DNA: The Risks
On the other hand, a lack of diversity can prove disastrous for any species. If you take plant breeding too far, the consequences can be dire indeed. This has been proven time and again in the history of breeding. The danger comes from crating monocultures: species consisting of only near-identical specimens with the same DNA.
If such monocultures encounter new diseases and pests, climate change, or other evolutionary pressures, they run a real risk of total extinction. That means no more new generations, and the end of its carefully bred genetic line. If that happens to your favourite haze strain, you’re out of luck. If it affects major food crops, as is currently happening with bananas for instance, it can lead to famine and widespread human misery.
This is the main reason for the expeditions of so-called strain hunters: they search for the original resilience of landraces to try and avert disasters like these. These adventurers are as likely to be hunting for ancient potato variants as for original cannabis strains.
Although breeders are a plant-loving lot, they tend to be less fond of evolution’s capricious nature, for understandable reasons. Firstly, evolution is a sluggish process: it took billions of years for the first living cells to evolve into worthwhile haze strains or successful growers, after all.
In a more concrete sense, growers can’t afford to wait millions of years until random mutations produce the specific new trait they are after. That is why breeders exchange the robustness of natural selection for the technical efficiency of goal-directed plant breeding.
Plant Breeding & Amsterdam Genetics DNA
This explains why breeders prefer to help evolution along; and this is the process we call plant breeding. Centuries of breeding experience have taught farmers and breeders much: we have been watching our crops reproduce long before we even knew that cells, DNA, and evolution existed. That is how we invented clever techniques to progressively develop the best traits of our most important plant species.
This also explains how we get to relish the taste of those gorgeously plump, sweet, and juicy red tomatoes with every evening meal. Moreover, after dinner, we get to enjoy the finest, strongest, tastiest cannabis strains that mankind managed to create. And best of all, you can find the finest examples of these carefully bred genetics in our online store: Amsterdam Genetics is at the apex of a long chain spanning millennia of evolution and professional cannabis breeding!
Each of our strains is the result of careful crossbreeding between historically successful strains, derived from ancient landraces through years of well-considered selection.. This, then, is cannabis plant breeding in a nutshell.
If you want to find out how you can direct this process of crossbreeding and selection for yourself, be sure to continue reading the next parts in our plant breeding blog series!