Talk:Gene flow
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Gene flow covers the movement of alleles between populations of cannabis: what counts as gene flow, how pollen, seed and people carry it, what it does to the populations it connects, the flow between hemp and drug-type cannabis and between feral plants and crops, and how it is measured. What persists of one lineage in another after hybridisation and backcrossing belongs to Introgression; how diversity is arranged among populations to Genetic diversity; the separate sexes that force cannabis to outcross to Dioecy; the loss of traditional populations to pollen from introduced cultivars to Genetic contamination.
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Discussion
Sources
- Ellstrand (2014), American Journal of Botany 101: 737–753: the definition of gene flow as successful immigration, set against dispersal; the effects of gene flow beside drift, selection and mutation; pollen against seed, and wind against animal pollination; breeders' isolation experiments, parentage analysis and estimates of Nm.
- Suarez-Gonzalez, Lexer and Cronk (2018), Biology Letters 14: 20170688: the definition of introgression used to mark the boundary with gene flow.
- Ren and colleagues (2021), Science Advances 7: eabg2286: 110 genomes; hemp and drug types on separate branches, with little gene flow between them during the crop's spread, and the best-fitting model with continuing gene flow from Chinese feral plants and landraces into both.
- Lynch and colleagues (2025), Nature 643: 1001–1010: a pangenome of 193 genomes; FST of 0.20 between drug-type and hemp populations, six inferred gene-flow events, and the route of drug-type cannabis to North America.
- Grassa and colleagues (2021), New Phytologist 230: 1665–1679: the independent breeding of hemp and drug cultivars and the deliberate crosses behind cannabidiol-rich cultivars.
- Woods and colleagues (2023), G3 13: jkac209: the transport of cannabis by people and the hemp crop of 1942–1945 in the United States.
- Wenger and colleagues (2020), American Journal of Botany 107: 1423–1432: feral cannabis in Minnesota, THC-type pollen donors, certified Canadian hemp seed above the THC limit, pollen drift and the 5 km isolation distance.
- Aina and colleagues (2025), Scientific Reports 15: 20423: 760 feral plants from 12 states, the dispersal of seed along roads, railways and feedlots, and the frequencies of the drug-type CBDA synthase allele.
- Aboulaich and colleagues (2013), Science of the Total Environment 443: 413–419: airborne cannabis pollen at Tétouan, 2008–2010, and pollen from the Rif reaching southern Spain.
- Bachir and colleagues (2022), Cannabis and Cannabinoid Research 7: 603–615: hemp and the drug-type plant in Morocco, pollen and fertile crosses.
Where the sources disagree
- When feral cannabis in the United States began. Woods and colleagues trace the present feral populations to the hemp grown in 1942–1945. Aina and colleagues date the escapes to cultivation between the 18th and 20th centuries and give hemp arriving in the Northeast as early as the 16th century; Wenger and colleagues tie the Minnesota populations to the wartime crop.
- Gene flow between the use types. Ren and colleagues found little evidence of gene flow between hemp and drug-type cannabis as the crop spread. Lynch and colleagues, with a different sample that includes cannabidiol-rich lines, inferred six gene-flow events among hemp and drug-type groups and relate them to breeding. The two studies sample different material and use different methods.
Terms
- Gene flow and dispersal. Pollen or seed that leaves a plant has been dispersed. It becomes gene flow only when it fertilises a plant or establishes and breeds in another population.
- Hemp and drug-type. "Hemp" here means fibre and seed cultivars and their feral descendants, the sense Grassa and colleagues use. Cultivars bred for cannabidiol, which some sources call "high-cannabinoid hemp", are called cannabidiol-rich cultivars or lines.