By Dr. Daniela Vergara
In this post I want to continue with the story about my recent publication on sex determination and expression Cannabis sativa (Baek and Vergara 2025).
How To Spot Cannabis sativa Plant Sex Early—Genes and Markers
Have you ever wished you could know if a cannabis plant was male or female before it started flowering? Well, we have a solution for you and it’s all based on the DNA.
Cannabis sativa plants don’t show their sex until they start flowering. This makes it hard for farmers and breeders who want to grow only female plants for their cannabinoid-rich buds. But there’s a solution: molecular markers.
What Are Molecular Markers?
Molecular markers are pieces of DNA that help tell the difference between male and female plants—before flowers appear. These are pieces of DNA that are found only on males others are found only on females and therefore serve as indicators for sex. Therefore, if we find a particular marker it tells us whether the plant will produce male or female flowers.
Some of these markers associated with males are the MADC1–MADC6. MADC stands for male associated DNA from cannabis. Some of these markers are very specific to males such as MADC2, which is known to show up in male plants and not in females. MADC3 and MADC4 are associated to DNA parts called “retrotransposons” (part of the “junk DNA and topic for a different story). MADC5 and MADC6 seem to be not that reliable as they were also found in female plants
So, to look for these markers in the lab tiny bits of plant tissue is needed for DNA extraction. If a male-specific marker shows up, the plant is most likely male. If not, it’s probably female.
Why It’s Tricky
Even though these markers are promising, they don’t always work on every variety of cannabis. That’s because cannabis strains can be very different from one another. A marker that works for one type of cannabis may not work for another.
Some markers also show up in both male and female plants, which makes things confusing. In addition, environmental factors may affect sex expression even if the DNA says one thing.
That’s why more testing across many different strains is still needed. Ideally, we would have universal markers that can be used on any cannabis plant, anywhere, and hopefully with more research we will get there soon!
Cool Fact
There are even some markers for female plants and monoecious plants (ones that have both male and female flowers on the same plant). These help farmers growing hemp for fiber or grain, where monoecious types are preferred.
In the future, early sex detection using DNA will help farmers:
- Save time and money
- Increase yields by focusing on females
- Avoid pollination mistakes
But…….
Did you know that a C. sativa plant can produce flowers of the opposite sex? While sex is mostly determined by the plant’s DNA and its chromosomes, as discussed in the previous blog post, the environment, which may alter plant hormones can have a big impact on how sex is expressed. That’s why C. sativa plants are said to have a labile or leaky sex expression.
Let’s break down how stress and chemicals can make a female plant produce male flowers (or a male plant produce female flowers) —and why that may be useful.
How Environment Affects Sex
Cannabis usually follows an XY sex chromosome system (like humans), but things like:
- Too much or too little light
- Extreme temperatures
- Stress from pruning or poor nutrition
…can change how genes get turned “on” or “off.” These changes can cause a female plant to grow male flowers or the other way around. This is called sex reversal.
Hormones at Work
Plants use hormones to grow and develop. Some hormones are key players in sex changes including ethylene and gibberellins.
Growers can spray C. sativa plants with certain substances that affect these hormones and trigger changes:
- Silver ion (in compounds like silver thiosulfate (STS), colloidal silver, or silver nitrate): Blocks ethylene, making a female plant grow male flowers. This is how feminized seeds are made!
- Ethephon: Releases ethylene and encourages female flower growth and it is specially useful if a male plant needs to produce female flowers.
Inducing female plants to produce male flowers helps growers make feminized seeds, which are almost always female.
The pollen produced by these female plants lacks a Y chromosome. When it fertilizes another female (or itself), the resulting seeds contain only X chromosomes.
Although this is useful because the feminized seeds, which are highly sought in the industry and can be sold for high prices, lack a Y chromosome and are almost guaranteed to be female. However, it may also pose challenges such as:
- These females may also produce male flower depending on the environmental conditions or if induced with the compounds described above.
- The Y chromosome, which is the largest in the entire genome as we described in our previous post, is lost, and perhaps there are important genes in the Y chromosome. In fact, in experiments comparing the pollen of true males to the pollen of those females that were induced to produce male flowers, the pollen of induced females was misshapen, and the germination rate of the seeds that used true male pollen was much better.
Further questions
Using chemicals to change sex comes with questions such as could this reduce genetic diversity, due to the lack of the Y chromosome? What genes are in the Y chromosome that make the pollen from true males better? Why are the seeds produced by the fertilization of true males more vigorous
All of these previous questions as well as understanding how the environment and hormones affect C. sativa’s sex expression will help us with plant cultivation and with breeding. Therefore, this knowledge could lead to improvement in better seedless flowers and to acquire more control over production.
References
Baek, Y. and D. Vergara. 2025. A review of sexual strategies in Cannabis sativa L. under genomic and environmental controls. Agrosystems, Geosciences & Environment 8:e70050.
