Talk:Introgression

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Discussion for: Introgression • View • Links • Related changes

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Page scope

Introgression covers the incorporation of one lineage's genes into another through hybridisation and backcrossing: how an introgressed genome forms, how introgression is traced in DNA, the cases studied in cannabis (cannabidiol-rich cultivars, feral populations in the United States, kif in Morocco) and adaptive and deliberate introgression. The movement of alleles between populations in general belongs to Gene flow; the loss of landraces and wild populations to introgression from introduced cultivars to Genetic contamination; the history of kif and the hybrid cultivars in the Rif to Cannabis in Morocco.

Data verification

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Discussion

Sources

• Suarez-Gonzalez, Lexer and Cronk (2018), Biology Letters 14: 20170688: the definition of introgression and of adaptive introgression, Anderson's coining of the term, ancestry assigned along chromosomes, the length of introgressed blocks and the evidence needed to show that introgression is adaptive.
• Ellstrand (2014), American Journal of Botany 101: 737–753: introgression as incorporation after hybridisation, within or between species; Anderson's Introgressive Hybridization (1949); highland maize and Zea mays subsp. mexicana; swamping and outbreeding depression.
• Lübberstedt, Beavis and Suza (2023), "Marker Assisted Backcrossing", in Suza and Lamkey (eds), Molecular Plant Breeding (Iowa State University Digital Press): the halving of the donor genome with each backcross, the formula for the recurrent parent's share, the five to eight generations of a breeding programme and linkage drag.
• Grassa and colleagues (2021), New Phytologist 230: 1665–1679: the CBDRx genome, ancestry proportions for CBDRx, Skunk#1 and Carmen, hemp ancestry on chromosome 7, the quantitative trait locus for the THC to CBD ratio and the selection scan.
• Lynch and colleagues (2025), Nature 643: 1001–1010: cannabidiol-rich lines in both drug-type groups of a pangenome; crossing beyond the northern European seed-oil gene pool.
• Ren and colleagues (2021), Science Advances 7: eabg2286: the ancestral gene pool and continuing introgression from Chinese feral plants and landraces into hemp and drug types.
• Wenger and colleagues (2020), American Journal of Botany 107: 1423–1432, and Aina and colleagues (2025), Scientific Reports 15: 20423: the drug-type CBDA synthase allele in feral cannabis in the United States and its two possible origins.
• Bachir and colleagues (2022), Cannabis and Cannabinoid Research 7: 603–615: hemp and the Moroccan drug-type plant, the introductions of 1980 and after, the two genetic studies of Moroccan cannabis and the proposal to sample herbarium material.

Where the sources disagree

• Where the drug-type alleles in feral hemp came from. Wenger and colleagues set out two arguments for impure historical hemp seed and one route for recent introgression, pollen and escaped plants from drug cultivation, and leave the question open. Aina and colleagues read several populations with an excess of intermediate or THC-type plants as possibly the result of introgression from recent drug cultivation, and propose genotyping herbarium specimens to settle it.
• What Moroccan sequences show. Bachir and colleagues report that El Alaoui and colleagues read the distinct THCA synthase sequences of 12 Moroccan resin seizures as coming from the newly introduced hybrids, while Onofri and colleagues found a variant shared by a Moroccan landrace and two Afghan accessions. The two studies sampled different material: resin seizures in one, a landrace in the other.

Terms

• Introgression and gene flow. Gene flow is any movement of alleles into a population. Introgression is what remains of one lineage in another after hybrids have been crossed back into it over generations.
• Naturalised. Grassa and colleagues call plants from non-cultivated populations "naturalised", leaving open whether a population is native, a recent escape or an old feral one.
• Recurrent parent. In a backcrossing programme, the parent to which the hybrids are crossed back in each generation; the other parent is the donor.

Images reserved in the article

One image has a place in the article but is not yet uploaded:

• File:Cannabis-introgression-backcrossing.jpg (lead, in the Genetics series box), a diagram to be drawn: a donor and a recipient chromosome pair, then the first hybrid and successive backcrosses to the recipient, with the donor's share falling from half to about a quarter and an eighth, and one short donor segment kept around a selected gene.