Same Strain, Different Smell: The Genetics of Cannabis Aroma

Watch the episode · 3:15

Two plants. Same strain, same seed pack. One smells like lemons; the other like a pine forest. The answer is hiding in a family of genes. And the most famous cannabis smell of all turns out not to come from terpenes at all.

Tiny perfume factories ▶ 0:23

Aroma is made in trichomes, the tiny glittering hairs on the flowers. Each one has a round gland head on top: a tiny perfume factory, packed with resin.

That resin is full of terpenes, the same aroma molecules found all over nature: limonene in citrus peel, pinene in pine needles, myrcene in mangoes and hops, and caryophyllene in black pepper.

More than a hundred terpenes have been found in cannabis. A typical flower carries around eleven in meaningful amounts, and that mix is its aroma fingerprint.

A spice rack of genes ▶ 1:02

Each terpene is built by an enzyme, and each enzyme comes from a gene called a terpene synthase. Researchers have found 55 of them in the cannabis genome. Think of them as a spice rack: which jars a plant has, and how much of each it uses, decides how it smells.

About half of these genes sit right next to each other in clusters, so they tend to be passed on together, like recipe cards stapled into a bundle. Inherit the bundle and you inherit a whole aroma style.

Source · Allen et al., PLOS ONE (2019)

Same strain, new nose ▶ 1:34

In a simplified picture, imagine a parent carrying one citrus bundle and one pine bundle. Cross two of those and the seeds reshuffle them: some get two citrus bundles, some two pine, most a mix. Same strain, different noses.

This also explains the labels from episode 6 on phenotypes. A 2021 study found that indica and sativa labels mostly track a handful of these terpene genes, not the plant's overall genetics.

Source · Watts et al., Nature Plants (2021)

The skunk surprise ▶ 2:06

Now, the surprise. In 2021, chemists analysed thirteen cultivars and found that the classic skunky smell barely comes from terpenes. It comes from sulfur compounds.

The key one is also found in hops, and a close cousin is what makes beer smell skunky when it is left in the sun. They are present in tiny amounts, but our noses are incredibly sensitive to them: a trace goes a very long way.

Source · Oswald et al., ACS Omega (2021)

Genes load the dice ▶ 2:35

Genes set the potential; conditions shape the result. Terpenes evaporate easily, so heat, light and how a plant is dried can all change the final aroma. Genes load the dice. The grow decides how they land.

Aroma is made in trichomes. Fifty-five genes build the terpenes, and they travel in bundles that reshuffle in every seed. And that skunky smell? Mostly sulfur.