Breeding Terms

Breeding Terms

Genetic material is inherited from both the pollen donor and mother plant. The genetic material, or deoxyribonucleic acid (DNA), is coiled into long, x-shaped strands called chromosomes and stored in the nucleus of every cell. In cannabis, each individual inherits 10 different chromosomes from the staminate pollen parent, and 10 different chromosomes from the seed mother or pistillate parent. The resulting individual has 20 chromosomes total; 2 copies of each of the 10 chromosomes, or 2 full genomes. This means there are 2 copies of every gene in the plant, one from the mother and one from the father. Each and every cell in the plant has a copy of this unique DNA compliment. The genetic code is written along the length of the chromosome strands, an each gene has a specific location along its length.

Phenotype

Phenotype is considered as the observable, qualifiable, or quantifiable representation of a given trait. Anything you can measure, categorize, or otherwise observe in an individual can be considered a phenotype. Every plant has many different phenotypes. For example, plant height might be broken down into three categories or phenotypes: short, medium, and tall stature. There is a short phenotype, a medium phenotype, and a tall phenotype.

Cannabis flowers demonstrate different color phenotypes as well. Most often we see green calyxes, but there are also plants that have purple calyxes. Sometimes there are even green calyxes with purple markings. These are all different calyx-color phenotypes. There are also calyx-size and calyx-shape phenotypes, or leaf size and shape phenotypes. Every trait has different phenotypes that can be selected for or against.

All phenotypes are the observable result of genes acting within the cells of the plant. Sometimes a single gene controls one trait (monogenic traits), and sometimes sets of genes operate together and contribute to make what we see as a phenotype (polygenic traits).

Genotype

The genotype of a plant is a way of describing the actual genetic condition that results in the phenotype. As the genetic constitution or makeup of an individual, genotypes are not always expressed. Some are latent and only express themselves given the proper environmental stimulus. For example, some plants have green leaves, but the leaves will turn purple under cold conditions. Other green-leaved plants will not turn purple even under cold conditions.

This happens because these plants have a different version of the gene(s) that control whether purple pigments are to be produced in the leaves. These different gene versions are called alleles.

These plants initially both had the green-leaved phenotype, but one plant developed an altered phenotype (purple leaf) in response to an environmental condition. This is due to an interaction of the genetics of the particular plant with respect to this trait (genotype) and the environment.

A simplistic way to think of the concept is:

Phenotype = Genotype + Environment

This isn’t 100 percent true. More accurately, the phenotype(s) seen in a given individual are the result of an interaction of the plant’s genotype with the environment.

There are always 2 alleles, or versions of every gene, including the gene responsible for stature. When we have 2 “s” (lower case) or “small stature” alleles, we see the short phenotype in the plant. Conversely, when the plant has 2 “S” (capital) or tall alleles, the phenotypic outcome is a plant of tall stature. If the plant happens to inherit a copy of the tall and short allele, the resulting phenotype is a plant of medium stature.

Often, breeders base the symbol for the genotype on the first letter of the recessive expression of a trait.

Homozygous/ Heterozygous

These are terms used in describing the genotypic condition of a plant, with regard to the similarity of the alleles for a given trait. If a plant is homozygous for a given trait, it has two copies of the same allele (homo=same). If a plant is heterozygous, it has two different alleles for a given trait (hetero=different).

Dominance

Consider two true-breeding varieties; a white pistil variety and a variety showing only pink pistils. Both conditions are true-breeding and therefore homozygous; in each case sexual reproduction of each group separately leads to only pink pistil or white pistil plants respectively. An F1 hybrid, or first generation cross of these two varieties, results in only white pistil plants; no pink pistils are seen regardless of how many F1 seeds are grown.

Upon sib mating of these F1 plants (crossing brothers to sisters, or mating F1 siblings), the resulting F2 generation produces 75% white pistil plants and 25% pink pistil plants. Notice the “disappearance” of the pink pistil plants in the F1 generation, and their subsequent “reappearance” in the F2 generation. In this case, white pistils are said to be dominant over pink pistils, and pink pistils are said to be recessive to white pistils.

Let’s consider the phenotypes seen, and provide symbols and deduce the genotypes:

P1 – White pistils x P2 – Pink pistils

F1 generation (all white pistil plants)

F1 male x F1 female

F2 generation (25% pink pistil plants, 75% white pistil plants)

Phenotypes: Pink (recessive) and White (dominant)

This 75% can be broken down into 2 genotypic classes, PP and Pp.

When we cross Pp x Pp plants, we get three possible combinations of genotypes. 25% PP, 50% Pp, 25% pp.

Therefore we know the 75% white pistil plants are actually 50% Pp + 25% PP, for a total of 75%.

Recessive

Recessive- An intra-allelic interaction such that an allele of one parent is masked by the presence of an allele from the other parent plant, in the expression of a given trait in the progeny. The recessive trait is not shown in the first generation of progeny (F1) but will reappear if siblings are mated, and the F2 progeny will result in 25% plants showing the recessive condition.

Dominant

An intra-allelic interaction such that the presence of an allele of one parent masks the presence of an allele from another parent plant, in the expression of a given trait in the progeny. Only the dominant trait is shown in the first generation of offspring. Of the F2 generation, 75% will also show the dominant condition.

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Breeding Terms

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