Understanding plant breeding terminology is essential for any hydroponic grower looking to work with genetics β whether you're selecting stable cultivars, interpreting seed bank descriptions, or breeding your own lines. This glossary covers the foundational terms used in plant genetics and breeding, from alleles and genotypes through to filial generations and self-pollination.
π± Core Genetic Terms
Allele
An allele is a specific version of a gene. Each gene can have multiple alleles, and the combination of alleles an organism carries determines which traits it expresses. Alleles are the fundamental units of heredity that breeders work with when selecting for desirable characteristics.
Genotype
The genotype is the underlying genetic code of an organism β the complete set of alleles it carries. Importantly, genotypes are not directly visible; only the phenotype is expressed and observable. Two plants can share the same phenotype but carry different genotypes, which becomes evident in the next generation.
Phenotype
A phenotype is any observable trait an individual expresses β growth structure, leaf shape, flower colour, yield potential, aroma profile. Phenotypes are determined by the genotype in combination with environmental conditions. In hydroponics, controlled environments allow phenotypic expression to be evaluated with greater consistency than in outdoor growing.
π‘ A-Grade Tip: When selecting phenotypes for breeding, run your plants under consistent environmental conditions β stable temperature, VPD, and light intensity β so you're comparing genetic expression rather than environmental response.
βοΈ Dominance & Expression
Dominant allele
When one allele masks or overrides another for the same gene, that allele is said to be dominant. Dominant alleles are represented with uppercase letters (e.g. T). A plant only needs one copy of a dominant allele to express the associated trait.
Recessive allele
A recessive allele is one that is suppressed when paired with a dominant allele. Recessive alleles are represented with lowercase letters (e.g. t). A plant must carry two copies of a recessive allele β one from each parent β for the recessive trait to be expressed.
Co-dominance
Co-dominance occurs when two alleles for the same gene are both dominant, and neither masks the other. Rather than one trait winning out, both alleles are expressed simultaneously, producing a varied outcome in successive progeny. Co-dominant alleles are represented with two uppercase letters (e.g. TV).
πΏ Zygosity: Homozygosity & Heterozygosity
Homozygosity
A homozygous individual carries two identical alleles for the same gene (e.g. TT). Homozygosity can occur naturally or be achieved deliberately through selective crossing. Homozygous lines produce highly consistent offspring, making them valuable as true-breeding parental lines in commercial and hobby breeding programmes.
Heterozygosity
A heterozygous individual carries two different alleles for the same gene (e.g. Tt). Heterozygous plants often display hybrid vigour (heterosis) but will not breed true β their offspring will segregate into different phenotypic ratios depending on the alleles involved.
π¬ Chemotype
A chemotype is a chemically distinct variant of a plant species β one that differs significantly in its secondary metabolites (such as terpene or alkaloid profiles) whilst showing minimal genetic variance and little to no observable differences in morphology or physiology. Chemotypes do not exhibit epigamic behaviour that affects physical appearance, making chemical analysis the primary method of differentiation.
π Breeding Generations Explained
P generation (Parental)
The P generation refers to the original parental lines used in a cross. When two P generation plants are bred together, they form true-breeding lines. True-breeding parental lines consistently produce the same phenotypic outcome across generations, as if self-pollinated.
F1 generation (First Filial)
"F" stands for filial. The F1 generation is the direct offspring of the first parental (P1) cross. F1 plants are typically uniform and often exhibit hybrid vigour, but they are not true-breeding β crossing two F1 plants together will produce variable offspring in the F2 generation.
F2 generation (Second Filial)
The F2 generation is produced by back-crossing (Bc) the F1 generation with the original parental line. F2 populations begin to segregate, revealing recessive traits that were masked in the F1 and providing breeders with a wider range of phenotypic variation to select from.
S1 generation (Self-pollinated)
"S" stands for self-pollinated. The S1 generation is produced by self-pollinating a filial generation to form a new parental line, which is then outbred into another line to create a new variety. S1 lines are a reliable route to stabilising genetics and establishing consistent true-breeding stock.
R1 generation (Reversal)
"R" stands for reversal. The R1 generation is formed via inter-sexing and/or inbreeding techniques that completely remove the male role from the breeding process. This approach is used to stabilise and consolidate genetics without introducing a separate male contributor.
π‘ A-Grade Tip: If you're working with purchased seeds, checking whether they're F1, F2, or S1 tells you a lot about what to expect β F1s will be consistent, whilst F2s and beyond will throw variation. Ask our team at A-Grade Hydroponics if you need help interpreting seed descriptions.
π What's Next
Plant breeding terminology forms the foundation of understanding how genetics shape every crop you grow. Whether you're selecting the best phenotype from a seed run or working towards a stable line, knowing these terms helps you make informed decisions at every stage.
Next week, we'll build on this glossary by exploring plant pedigrees and the terms that go hand in hand with what we've covered today. In the meantime, browse our range of propagation supplies and cloning equipment at A-Grade Hydroponics β the right tools make a difference from the very first generation.
