Zygote or zygous is derived from the greek term “yolk”, so thinking about the implications of heritability in genes in comparison to differences in zygosity means thinking about “different yolks of the same egg”. These “different yolks of the same egg”, called alleles, are the genetic material which dictates physical expressions of specific traits such as plant height or leaf shape. The zygosity of said alleles can vary due to specific heritability factors indicative to that chemovar. Homozygous refers to the heritability of alleles to only be expressed in one sense, for instance, only short plants. Heterozygosity refers to the ability of specific alleles to be expressed differently based on the dominance factors of the donor (male) parent. For example, if a parent, having two dominant copies of the same allele in a given loci, breeds with an individual with the same quality, then their offspring will have dominant heritability for this trait. Or, if the stated individual has two recessive copies of this trait at a given loci (homozygous recessive), and breeds with an individual with different copies of this allele, gene actions will favor the homozygous recombinant pair 50% of the time. With these odds, one can quickly see why selecting two homozygous parents betters the chances of developing genotypically- and phenotypically-predictable chemovars.
To develop a novel, true-breeding strain, an interspecies cross of landrace cannabis is the only route. True-breeding is a quality inherent to the F1 or first filial generation of seeds produced by pollinating Cannabis sativa L. and Cannabis indica L. The first filial generation refers to the first offspring of the parent generation. An individual amongst a population of cannabis plants may express what are thought to be highly dominant Sativa or Indica characteristics, such as leaves with broad margins (indica) versus long and thin (Sativa). This individual can still transmit undesirable alleles even if propagated from a “stable” (predictable and homozygous) germplasm, due to the fact that a stable line is not true-breeding, and therefore chance transmission of unwanted alleles is possible, a scenario which could result in unwanted growth patterns or plant performance. It is important to note that unwanted alleles do not always translate into negative outcomes. For instance, a plant could sacrifice yield for higher pathogenic resistance or flowering time for a more petite taxonomy. Although, these traits are beneficial to the plant, they could interfere with the objectives of the breeder.
The odds of developing a phenotypically-consistent F1 from a stable line are much higher in homozygous than in heterozygous gene pools due to the heritability factor in the cannabis species. In a broad sense (controlled environment), this relationship can be described by the following equation: H2= VG / VG + VE, where H represents the heritability, VG represents variance due to genotype and VE represents variance due to the environment. This equation takes into account actual genetic heritability versus environmentally-induced factors. So what is the take home here? If your chemovar is suspected (in lieu of genetic testing) of homozygosity for a desirable trait at a certain loci and you want to enhance this quality through breeding, limit as many environmental factors (narrowing broad sense heritability) as possible. Then the chances of said trait being expressed in filial generations increases significantly.