Sex in the Garden
Part Two: Basic Breeding Concepts
By: Paul Josephs
This part in the series will look at what happened with our hypothetical hybrids from part one. In part one we crossed two hybrids from seed stock and now we will grow that second generation hybrid to maturity. We will look at the offspring and learn why certain results occurred.
Our cross was between two hypothetical strains, Mystery Magic and Cannabis King’s Conquest. Our goal is to create a strain that has a compact structure, an intriguing taste and a strong effect. We thought purple coloration would be a plus. Mystery Magic was described as a very compact, indica-dominant hybrid with frosty buds and some of its progeny would exhibit purple calyxes. King’s Conquest was described as a vigorous and potent strain with an exotic aroma and taste from Kush and South African genetics. We selected a Mystery Magic female with purple calyxes and crossed it with a compact King’s Conquest male. We named our new hybrid King’s Magic. From those resulting seeds we grew out a number of plants and selected the male and female that best represented our goal and crossed them.
What We Saw
We were intrigued and surprised by the first generation (F1) results. Although one of the parents had purple genes, none of the F1 plants exhibited purple calyxes. Without losing hope for purple plants later, we selected two robust plants to cross from the F1 generation and made a lot of seeds, which we grew out as the second generation (F2). We grew as many F2 plants as we could and with some grower friends helping out we have 80 plants to evaluate. 30 are males and 50 are females. Of the 50 females, 13 have purple calyxes and the 37 remaining do not.
Let’s focus on the purple calyx trait and trace it through our project so far. In the original parent generation the Mystery Magic plants had two of five plants with purple calyxes and we picked one to breed. The King’s Conquest male we picked to breed with had no pigmentation. When we flowered out the resulting F1 plants, none showed the purple color, but the gene must be there from the Mystery Magic mother, right? We don’t think King’s Conquest has that gene, as the purple trait wasn’t exhibited in any of the King’s Conquest females. When we made the F2 generation the purple shows up again in approximately 25 percent of the offspring.
Why did that happen?
We just witnessed genetic recombination and expression. The F1 generation combines half of the chromosomes from each parent to make up a full set in the resulting seeds. I like to think of the process as a zipper. The DNA of each parent makes a complete zipper. The exceptions are sexual cells, the pollen of the male and the ovule of the female, which each carry only one half of the paired genes. These are like two different but compatible halves of a zipper. When fertilization occurs, the two different halves zip together to make a new full set of gene pairs. This means the next generation shares one-half of the genes of both parents in their DNA.
Dominant and Recessive genes
Genes for specific traits, like purple calyxes, can be dominant or recessive. Dominant genes express themselves in offspring even if only one-half of the pairing is dominant. Recessive genes need to make up both halves of the pairing to be expressed in the plant. Since none of our F1 plants showed the purple coloration, it is reasonable to believe that is a recessive trait. The female Mystery Magic mother we selected must have had both genes for purple calyxes paired to express the trait. The King’s Conquest male did not have that gene, and the green calyx gene pair it carries is dominant, therefore none of the F1 plants exhibited that trait, even though each gene pair for calyx color had one dominant green gene and one recessive purple gene in it.
F2 mix and match
When we crossed the two best F1 plants of our new hybrid we unzipped the DNA and then re-combined the resulting half zippers in the resulting F2 seeds. Now the gene pairs are more diverse. A percentage will have only the dominant green calyx genes paired up, a percentage will have the half and half green and purple pairs and a percentage will have the recessive gene paired up. We noticed that 13 of the 50 females in our F2 generation showed the purple trait, which is approximately 25 percent. In genetics classes and texts a popular tool to show percentages of gene pairs is the Punnett square. A Punnett square for the gene combination we are looking at would show 25 percent dominant/dominant (green/green) genes, 50 percent dominant/recessive (green/purple) genes and 25 percent recessive/recessive (purple/purple) genes. Our cross verifies this recessive expression of 25 percent purple calyx plants.
Now we have a better grasp of what happened at the gene level in our breeding project, and we were introduced to some terms and concepts. In the third installment of this series we will explore how to fix a trait and make a strain ‘breed true’ for that trait and also see how this breeding project could go in different directions.