Topophysis is a position effect in vegetative propagation: a cutting can carry on behaving like the part of the plant it came from for some time. Cuttings from lower, shaded or older branches may root, grow or flower differently from cuts taken at the top, even though they share the same genotype.
In practice
Cannabis growers see it as variation between clones of one mother. Cutting position measurably changes rooting in cannabis stem cuttings (Caplan et al. 2018). Growers also report differences in vigour and early growth that fade after a cycle or two.
House position: cuts taken from different parts of a plant can behave differently. That may or may not involve mutation. Practical advice is to take cuts from consistent locations on the mother (similar height, branch age and size) so that clones start alike, and to judge a cultivar on several clones, not one.
Don't confuse with
- Genetic drift: random change in allele frequencies in seed populations; clones do not drift.
- Somatic mutation: a real DNA change in one branch; rare, and a mutation doesn't mean a loss.
- Pathogen decline: a cut that gets worse every cycle is a disease or care problem, not position.
Cloning is propagating a plant by rooting cuttings from it, producing new plants that are genetically identical to the donor.The genotype is the set of alleles a plant actually carries, either at one locus or across its whole genome, as opposed to the traits you can see.The programmed ageing and breakdown of leaves and other tissues, in which the plant recycles nutrients (especially nitrogen) from old leaves to developing flowers and seeds.Genetic drift is random change in allele frequencies between generations of a seed population, strongest in small populations; clones do not drift this way.An allele is one version of a gene; a diploid cannabis plant carries two alleles at each locus, one from each parent, which may be the same or different.Somaclonal variation is genetic or epigenetic change that appears in plants regenerated from tissue culture, especially from callus, making them differ from the donor plant.A mutation is a change in a plant's DNA sequence, arising in seed or in one branch (a somatic mutation); mutations are rare and usually neutral.A clone-only is a cultivar that exists only as cuttings from one original plant, with no seed line that reliably reproduces it.
