If you’re reading this, you’ve probably already created some crosses and maybe even some interesting phenotypes. But to move from random breeding to deliberate improvement, we need to understand how traits are actually passed from parents to offspring. Let’s get into the science while keeping things practical.

The Fundamentals Matter

Think about it - when you make crosses, you’re essentially shuffling genes between plants. But this shuffle isn’t random like a deck of cards. It follows specific patterns that Gregor Mendel first discovered while working with peas. Understanding these patterns lets us predict outcomes and make smarter breeding decisions.

Simple vs Complex Inheritance

Some traits in cannabis follow simple inheritance patterns. Take CBD:THC ratios - they’re controlled primarily by a single gene with multiple variants (alleles). When you cross a high-THC plant with a high-CBD plant, you can predict the ratios you’ll see in the offspring based on whether these alleles are dominant or recessive.

But most traits that breeders care about - yield, potency, terpene profiles, growth structure - are complex. They’re controlled by many genes working together, plus environmental factors. This is why you can’t just cross your two best plants and expect all the offspring to be as good or better than the parents.

Understanding Population Genetics

Here’s where many home breeders go wrong - working with populations that are too small. If you’re starting with just a few plants, you’re severely limiting the genetic diversity you have to work with. The key to successful breeding is starting with large, diverse populations and systematically selecting the best individuals over multiple generations.

Let’s break down a practical example: Say you want to increase trichome density. This trait is influenced by multiple genes, so you need to:

1. Start with a large population (100+ plants if possible)
2. Select the top 10-15% with the best trichome coverage
3. Cross these selections (more on breeding schemes in another post)
4. Grow out the progeny and repeat the process
5. Keep detailed records of each generation’s performance

This methodical approach, while requiring more time and space than simple pollen chucking, will result in actual genetic improvement rather than just random variation.

The Role of Dominance and Recessiveness

Understanding dominance relationships is crucial. When a trait is dominant, it will show up whenever that gene variant is present. Recessive traits only show up when an individual inherits the recessive allele from both parents. This is why sometimes crossing two excellent plants can produce offspring that express undesirable recessive traits - those genes were always there, just masked by dominant alleles. I’m not saying recessive traits are undesirable - they’re just harder to select for.

Testing Your Breeding Lines

To really understand what you’re working with, you need to test your breeding lines. This means:

• Growing out enough progeny to see the range of variation
• Testing crosses with different partners (test crosses)
• Evaluating performance under different conditions
• Keeping detailed records of everything

Moving Forward

As you develop your breeding program, focus on:

• Maintaining good population sizes
• Using systematic selection methods
• Keeping detailed records
• Understanding the inheritance patterns of your key traits
• Testing your lines thoroughly

In the next post, we’ll take a deeper look into qualitative versus quantitative traits and how this distinction affects breeding strategy. Understanding these concepts will help you make more informed decisions about which breeding methods to use for different breeding objectives.

Points to Ponder in the meantime:

1. What traits are you currently selecting for in your breeding program?
2. How large are your breeding populations?
3. What unexpected traits have you seen emerge in your crosses?

Remember: Successful breeding is about more than just combining good parents - it’s about understanding and manipulating inheritance patterns to achieve your goals systematically.

References

1. de Meijer, E. P. M., Bagatta, M., Carboni, A., Crucitti, P., Moliterni, V. M. C., Ranalli, P., & Mandolino, G. (2003). The inheritance of chemical phenotype in Cannabis sativa L. Genetics, 163(1), 335-346. https://doi.org/10.1093/genetics/163.1.335

2. Weiblen, G. D., Wenger, J. P., Craft, K. J., ElSohly, M. A., Mehmedic, Z., Treiber, E. L., & Marks, M. D. (2015). Gene duplication and divergence affecting drug content in Cannabis sativa. New Phytologist, 208(4), 1241-1250. https://doi.org/10.1111/nph.13562

3. McKernan, K. J., Helbert, Y., Kane, L. T., Ebling, H., Zhang, L., Liu, B., Eaton, Z., McLaughlin, S., Kingan, S., Baybayan, P., Concepcion, G., Jordan, M., Riva, A., Barbazuk, W., & Harkins, T. (2020). Sequence and annotation of 42 cannabis genomes reveals extensive copy number variation in cannabinoid synthesis and pathogen resistance genes. bioRxiv. https://doi.org/10.1101/2020.01.03.894428

4. Campbell, L. G., Dufresne, J., & Sabatinos, S. A. (2020). Cannabinoid inheritance relies on complex genetic architecture. Cannabis and Cannabinoid Research, 5(1), 105-116. https://doi.org/10.1089/can.2018.0015

5. Grassa, C. J., Weiblen, G. D., Wenger, J. P., Dabney, C., Poplawski, S. G., Motley, S. T., Michael, T. P., & Schwartz, C. J. (2021). A new Cannabis genome assembly associates elevated cannabidiol (CBD) with hemp introgressed into marijuana. New Phytologist, 230(4), 1665-1679. https://doi.org/10.1111/nph.17243

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[This post assumes legal hemp/cannabis breeding in compliance with all applicable laws and regulations.]