Basic nomenclature of cannabis genetics

What are IBL, S1, BX, F2 or landrace cannabis plants?

Hindu Kush by Sensi Seeds

Hindu Kush by Sensi Seeds

Often, when it’s time to buy cannabis seeds, the beginner grower can quickly become confused by some of the acronyms that are written next to the name of the variety. Simply by learning some basic concepts you’ll be able to make the correct choice between seeds with the same name, but different acronym.

There is a big difference between acquiring a second filial generation (F2) or an IBL, even if we talk about seeds of the same variety. These differences will condition the growth pattern of the plants, and also the final product, so that it is almost essential to learn exactly what is the meaning of these acronyms to be more accurate in choosing which seeds to buy, saving ourselves deceptions and getting closer to our preferences.

Pure varieties

Also known as landraces or purebreds, pure cannabis varieties have been the basis of cannabis breeding over the past decades. These species are endemic to a geographical area, where they have developed without having been crossed (hybridised) with other varieties. There are a large number of landraces from all around the planet, belonging to any of the three families of cannabis, C. sativa, C. indica and C. afghanica. Nepal is a good example; in this country different pure cannabis varieties (mostly narrow-leaved mixed use varieties) are grown and you can easily see the differences between genotypes based on the height above sea level at which they are cultivated.

Each variety expresses its genetic code (genotype) with a certain growth and flowering pattern (phenotype), so that pure varieties – with a purest genotype – show great uniformity, with just a few slight differences between phenotypes. We can expect very little variation between landrace specimens of the same variety, giving plants with very similar growth, organoleptic and psychoactive traits. Good examples of these varieties can be Hindu Kush (Sensi Seeds), Colombia Punto Rojo (Cannabiogen) or China Yunnan (Ace Seeds).

IBL or stabilized cannabis hybrids

F1 Hybrid

F1 Hybrid

The IBL acronym (in-bred line), means that the cross was made using plants with almost identical genotype (inbreeding). On the contray, outbreeding is employed to introduce new genes into the variety. Although it happens naturally, self-pollination is a common technique used by breeders to fix desirable traits and thus stabilise the genetic line, either with landraces or hybrids. In cannabis genetics IBL seeds should present a highly uniform growth. Classic IBL examples are Skunk and Northern Lights (Sensi Seeds) or White Widow (Greenhouse). There is a lot of work behind IBL’s like these, as a large population of pure specimens had to be used to select the correct parents. In addition, the breeder must fight against inbreeding depression, the result of crossing parents with very similar genetic information. The reward for this job made properly is a highly stable seed variety.

If we make a cross between two different landrace or IBL lines (parental A and B) with different genotypes, the resulting offspring will be the F1 hybrid, the first filial generation from the cross of the phenotype #1 (Parent A) with the phenotype #2 (Parent B). Commonly in this kind of crosses we will observe a very uniform offspring, depending on how stable the parents are, of course. The F1 hybrid between two pure varieties or IBL’s will show the so-called hybrid vigour – also known as heterosis or outbreeding enhancement – introducing new genes that will produce “better” specimens.

Varieties like Orient Express (Ace Seeds), Red Afro (Tropical Seeds) or Eddy from Original Delicatessen would be good examples of true F1 hybrid. Thus, we refer to the first filial generation of any cross as an F1, while the term “F1 hybrid” is used when the parents are different landrace or IBLs.

How to create a polyhybrid

How to create a polyhybrid

When we cross two F1 individuals (whether landraces, hybrid or polyhybrid varieties), we obtain the second filial generation or F2, and so on with next generations, F3, F4, etc. The second filial generation often gives a more heterogeneous offspring than the F1; we can expect 25% to resemble parent A, 25% to resemble parent B and 50% will be a mixed expression of traits from both parents. As a  consequence the stabilisation work must continue generation after generation ( F3, F4, F5…) until we find the generation that gives a uniform offspring with the traits that we are seeking.

Many of the seeds that we can find in shops are polyhybrids, crosses between different hybrids. The offspring of such crosses are in many cases quite unstable, producing plants with very different traits. Keep in mind that in these cases, the genetic mix is very varied, so we can not expect polyhybrid offspring to be as homogenous as an F1 hybrid. It’s easy to imagine how complex it can be to stabilise a cross, since we are mixing different genes from different varieties, which makes the selection and stabilisation process of the different traits a very hard work. The vast majority of hybrids on the market are in fact polyhybrids, like the White Russian (Serious Seeds) or Fruity Jack / Jack el Frutero (Philosopher Seeds).

BX or Backcross

Backcrossing is a common technique used by breeders to fix certain traits. This is done by crossing one of the progeny (F1, F2…) with one of the original parents (recurrent parent) which has the desired trait. To have an even more stable expression of the desirable trait, you can cross the BX1 again with the recurrent parent to have a BX2 (squaring) and so on with BX3 (cubing), BX4, BX5…



This technique is also used to replicate clones in seed form. It is done by choosing a male parent to cross with the clone only, backcrossing it as many times as needed to get an offspring as similar as possible to the original clone. The Apollo 13Bx (TGA Subcool) is an excellent example of this technique.

Tropimango by Philosopher Seeds

Tropimango by Philosopher Seeds

S1, feminised cannabis seeds

The acronym S1 refers to the first filial generation produced as a result of crossing the plant with itself. This is achieved by a range of techniques aimed at reversing the sex of the selected female plant, getting it to produce male pollen and using it to pollinate itself. If it’s done properly, we get feminised offspring with the same genotype of the parent used.

As always in genetics, the more stable the parent is, the more stable the offspring will be. This technique can also be used as a regular backcross, selecting and fixing traits but starting with just one parent. Thus, we can find S2 or S3 seeds, which have been backcrossed again with the original parent. Examples of S1 are Tropimango (Philosopher Seeds), S.A.D. (Sweet Seeds) or Trainweck (Greenhouse).


22 comments on “Basic nomenclature of cannabis genetics

  1. Daniel S Lennox

    Hi All, I just want to ask if anyone ever tried using medical cannabis as an alternative meds? I have read many articles about medical marijuana and how it can help you in terms of chronic pain, bone injuries, eating disorder/anorexia, anxiety disorders and panic attacks, inflammation, even cancer and a lot more. Cbd and thc are also new to me and I don’t even smoke. If this is true I cant find any solid conclusive evidence that speaks to its efficacy. Any personal experience or testimonial would be highly appreciated. Thanks

    1. Tim Alchimia

      Hi Daniel, thanks for your question, sorry for taking so long to answer, I’m afraid it must have slipped through the net! In answer to your doubts, yes! Many people worldwide have experienced huge success using cannabis as an alternative to pharmaceutical treatments. There is an ever-expanding library of online articles and studies into this subject and as the legal situation improves in the USA we can expect to see even more scientific evidence as to its efficacy. Have a look at the section of our blog that deals with Medical Cannabis and if you have any more questions then leave a comment for us on the appropriate post. All the best!

  2. Dennis

    How do we find F1 seeds, can we trust the seed company? As I have never seen a seed company that says F1 seed, just the names that they Sell.

    1. Tim Alchimia

      Hi Dennis, thans for your question, you’re right, it’s not common to see that kind of information on cannabis seed packs or catalogues. This is probably because most cannabis breeding isn’t carried out by qualified geneticists specialising in botany, but by enthusiasts and veteran growers, meaning that much of the terminology employed by professional geneticists is either misused or not understood in the cannabis seed indusrty. A true F1 hybrid should be a cross using two different, pure varieties, however much of what cannabis breeders refer to as “F1” are crosses between hybrids or polyhybrids and so are not strictly “true F1” hybrids.

      If you’re looking for good F1 hybrids from reliable and trustworthy breeders, from my own personal experience I can recommend three Spanish seed banks: ACE Seeds, Cannabiogen and Tropical Seeds, and also a great French seed bank Underground Seed Collective, all of whom do some great work with pure landrace genetics, producing some spectacular F1 hybrid seeds. I hope that helps, all the best!

  3. Ripper

    No tim an f1 is a cross between two different cannabis strains.

    1. Tim Alchimia

      Hi Ripper, thanks for your comment. That’s pretty much what I was saying, a true F1 is a cross between two genetically distinct but true-breeding pure lines. My point is that you can’t cross two modern poly-hybrid strains together and call the progeny a true F1. All the best.

  4. Mike H

    Hi, Tim- How would an enthusiast breeder fix the genotype to produce both a homozygous male and female before crossing? As you know cannabis is dioecious. The goal is to produce uniformity in the F1 generation. Is backcrossing the best way to go? I can’t seem to understand how backcrossing would be able to introduce desirable traits from the female if the donor is the male. Great article!

  5. xyz

    not sure if i understand the question correctly..but there is much more than just crossing..main work is selection .

  6. Nicolas

    Hey Tim, then how would you call a “F1” cross between two diferent Hybrids?

    1. Dani Alchimia Post author

      Hi Nicolas,

      Tim is on holidays, so I’ll reply your comment. Well, since “F1” theoretically means “first filial generation”, I often call my crosses “F1” no matter if they come from a single landrace, from two different landraces or from hybrids. Some people will tell you that it only stands for a cross between two different landraces, although most breeders call the first filial generation “F1” regardless the genetics/parents used to develop it.

      Hope it helped!

  7. D Watson

    You say STRAIN in this article but that is not a correct term for Cannabis which has seed Varieties or clone Cultivars, you also say Cannabis Indica, Sativa and Ruderalis but the proper taxonomic terms are WLD wide leaf drug, NLD Narrow leaf drug, both are Cannabis Indica, all hemp is Cannabis Sativa, no one is sure about Ruderalis if it a third variety or is just escaped cultivated varieties.
    Before you attempt to teach you should learn the real terms to use.

    1. Tim Alchimia

      Hi Sam, thanks very much for your input, it’s really very much appreciated. I’m going to edit the post to replace the term “strain”, that’s a good point, thanks for pointing it out. This article was originally written in Spanish and later translated to English, so that may explain it to a certain extent.

      Believe it or not, we’re fully aware of the terms proposed by Karl Hillig, (just to confirm, should it be BLD Broad Leaf drug or WLD Wide Leaf Drug? I’ve seen both used) and while we do sometimes use these terms where appropriate (and we’d like to use them more), we’re not writing scientific studies here, we’re just trying to inform and help out your average home-grower.

      I agree, it’s important to be educated in order to educate others, but I also think a balance needs to be struck between strict scientific accuracy on one hand, and accessibility of information on the other, we need to present things in way that can be easily understood, without requiring too much additional explanation: everyone knows what we’re talking about when we say “Sativa, Indica or Ruderalis”, and as I’m sure you’re aware, most growers couldn’t give two hoots about using the proper botanical terms, indeed some are proud of not using them!

      It’s an interesting subject, and one that we’ll probably address in another post fairly soon. I’m all for teaching our readers the correct terms to use when talking about cannabis, but whether they actually use it or not is another matter. Like they say, you can lead a horse to water…

      Thanks again for taking the time to comment, all the best!

  8. D Watson

    BTW there are no Homogenous varieties being sold, all cannabis is Hetrogenous, and as Cannabis is a dioecious obligate outcrosser that will not change soon.

    1. Tim Alchimia

      Hi again Sam, and thanks for the comment.

      OK, so if I understand this correctly, we should be talking about uniformity in cannabis plants rather than using the term “homogeneity”? I get that in genetic terms there’s a difference, and that cannabis isn’t homozygous, it’s heterozygous, but can we not describe plants as homogeneous in appearance and behaviour?

      Personally, I’d argue that homozygous and homogeneous aren’t the same, they mean two different things, with homozygous referring to a gene having two matching alleles, while homogeneous, which as far as I know is not a term with a genetic basis, refers to uniformity.

      I think it’s probably fair to describe as homogeneous a seed variety that consistently produces plants with an almost identical appearance, behaviour, terpene profile and effect, even if it isn’t homozygous, genetically speaking. Is this wrong?

      All the best and thanks again for your contribution.

  9. S Holmes

    D Watson. Your self-assured-ness is worrying. Perhaps Afghanistan has had a deeper impact on you than I first thought.

  10. C. Doyle

    It’s elementary Watson

  11. MichiGreen

    Many breeders today are crossing 2 strains of cannabis to create a new strain that they sell. From reading this article it appears that they are probably both hybrid parents and not likely to create a true F1 strain that would show hybrid vigor and the best traits of both parents. More likely, the seeds produced would show a wide variety of genetic traits (unstable) and be unsuitable for breeding unless a large number are grown and the succeeding generation parents carefully selected. Am I correct in this line of thinking? Or are these multitudes of “breeders” actually producing seeds that will show stability and expected qualities?

    1. Tim Alchimia

      Hi MichiGreen, thanks for your comment. In short, yes you’re correct. The vast majority of seeds available these days are poly-hybrids, or poly-hybrids of poly-hybrids! Cannabis trends/fashions and the speed they move mean that very few seed banks are willing to put in the work required to properly “stabilise” a strain before releasing it, preferring instead to simply cross one hype clone with another and release the results. For the most part it seems to matter little, as many growers these days are happy to “pheno-hunt” for a spectacular example, different to anything anyone else has, that they can clone for future crops, rather than expecting to sow 10 seeds and end up with ten almost identical, “stable” plants.

      However, with the advent of legalisation in different countries around the world, it’s more likely that good, conscientious breeders will be able to make careful selections from large populations of plants to breed with. Hopefully we’ll see some progress in that direction and get some stable seed lines.

      All the best, happy growing!

  12. Aaron

    Hi Tim, Is it still labeled a F1 if a female was open pollinated outdoors and the male is unknown? Or, would it be considered an heirloom? I’m just trying to correctly label my seeds and keep track of the generations. Thanks!

    1. Tim Alchimia

      Hi Aaron, thanks for your question. Strictly speaking, a true F1 would be a cross between two unrelated, stabilised (inbred) lines, however, these days the cannabis world uses the term for any cross between two different plants. In this case, I’d probably label the cross F1 OP (for open pollination) just for clarity. Hope that helps, all the best and happy growing!

  13. Keith H

    Hello Tim i love the post but there are a few questions i did not see answered in the post. Lets say i have a f1 hybrid or any strain for that matter and i want to stabilize it. I have picked out a nice mother plant with traits i want what criteria do i use to for the male plant? all the one i have ever grown are tall and lanky . How would i know what kind of traits the male plant would produce before I pollinate it to a female?

    1. Tim Alchimia

      Hi Keith, thanks for leaving your comment and question. Yes, males will usually tend to be more tall and lanky than female plants, I’d imagine that this is a trait that evolved to allow them to stand over the females and spread their pollen further than if they were the same size as them.

      As for selecting a male, it’s not an easy process. You can start choosing plants based on visual and olfactory traits such as structure, colour, leaf shape and aroma when rubbing the stem, selecting the individuals with traits that match the mother plant you want to stabilise.

      Unfortunately, though, there’s no short cut when it comes to knowing what traits the male will pass on to the offspring. The only way to be sure is to make seeds and test the progeny, which is a long and potentially costly process.

      Another option would be to make a backcross of your mother plant. This involves making an initial outcross with a different male and then pollinating the mother with the males from this first outcross, creating the BX1 generation (backcross). Maes from this BX1 generation could then be used to pollinate the mother again, creating the BX2 generation, and so on, in a process known as “cubing”.

      I hope that’s answered your doubts, if not please let us know. All the best and happy breeding!

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