Watch the episode · 3:04Pick up a pack of seeds and you will see codes like F1, S1 or BX3. They are not marketing fluff. Each one tells you exactly how those seeds were made, and how much the plants will vary when you grow them.
The first cross: F1 and hybrid vigour ▶ 0:21
Most strains start as a cross between two different parents. Breeders write the mother first and the father second: mother × father.
Picture one gene. If one parent carries two copies of one version and the other parent carries two copies of another, every seed gets one of each. That is the F1, the first filial generation.
From truly pure, inbred parents, F1 plants come out remarkably uniform, and often stronger than either parent. That is called hybrid vigour. But most cannabis parents are not that pure, so a cannabis F1 can still vary.
F2: the genetic lottery ▶ 1:00
Cross two F1 siblings and you get an F2. Now the genes reshuffle: some plants lean towards one grandparent, some towards the other, and some sit in between.
Hidden recessive traits can reappear too. That is why F2 seeds are prized by breeders hunting for something special, and less predictable for everyone else.
IBL: breeding true ▶ 1:23
An inbred line, or IBL, starts with a cross. Then the breeder keeps selecting the plants that best match the goal, breeding them together, and doing it again and again for many generations.
- 01Cross
two parents
- 02Select
keep the plants that match the goal
- 03Inbreed
breed the best together
- 04Repeat
for many generations
Each round, the variation shrinks. The end result breeds true: seeds that grow up looking and behaving like their parents.
S1: a plant crossed with itself ▶ 1:46
Remember the reversed female from episode 1 on feminised seeds? If she pollinates herself, her seeds are S1: selfed. Every seed is feminised, and every seed comes from a single plant.
That makes S1 seed a way to preserve a favourite plant in seed form. But selfing also exposes hidden recessive traits, so S1s can still surprise you.
BX: backcrossing to a parent ▶ 2:12
A backcross, or BX, crosses a plant back to one of its own parents to lock in that parent's traits. Each round brings the offspring closer: after one backcross about 75% of its genes come from that parent on average, after two 87.5%, and after three nearly 94%.
on average: each backcross halves what's left of the other parent
F1 is the first cross. F2 reshuffles the genes. An IBL is bred for generations until it breeds true. S1 is a plant crossed with itself. And BX goes back to a parent. To see how breeders combine all of these into a brand new variety, read how a new cannabis strain is made.
Sources
This episode explains standard plant-breeding genetics covered in the earlier episodes.
Every claim in this article comes from the episode script, which is checked against these papers. Prices on Seedscanner are dated observations; this page is not growing or legal advice.
