Talk:Genetic drift
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Genetic drift covers random change in allele frequency: the sampling of genes between generations, fixation and loss, the loss of heterozygosity, founder events and population bottlenecks, drift beside the other forces that change allele frequencies, and cases in cannabis where drift or small population size has been proposed: small feral populations, breeding lines and the regrowing of seed collections. The size that sets the rate of drift, and the plant numbers genebanks aim for, belong to Effective population size; the balance of drift against selection to Natural selection; migration to Gene flow; the division of variation among populations to Genetic diversity; inbreeding depression to Outcrossing.
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Discussion
Sources
- Felsenstein, Theoretical Evolutionary Genetics (text of December 2019), pp. 251–263, 269–270, 283, 289–290 and 326–328: drift as the random change of gene frequency from Mendelian segregation and offspring number, and its identity with inbreeding in a finite population; Hagedoorn and Hagedoorn (1921), Chetverikov (1926) and Wright (1929, 1931); the Wright–Fisher model; the loss of 1/(2N) of heterozygosity a generation and its half-life; fixation probability equal to initial frequency and the growth of variance among populations; the weight of a few small generations; drift as the random force beside selection, migration and mutation; mutation and drift (2Nu); the rapid loss and slow recovery of variation after a bottleneck; the 4Ns criterion.
- Davinack, Molecular Ecology & Evolution: An Introduction (2024), pp. 110–122: drift and its effects in small populations; the founder effect; bottlenecks and their lasting effect; the loss of favourable and persistence of harmful alleles in small populations.
- Aina and colleagues (2025), Scientific Reports 15: 20423: the five genetic clusters of 346 feral plants in the United States; the low heterozygosity of the New York cluster and the authors' suggestion of small size and isolation; local drift in populations near Hardy–Weinberg equilibrium.
- Woods, Price, Matthews and McKay (2023), G3 13: jkac209: segregating sites and Tajima's D in Asian, European, feral American and drug-type cannabis; the authors' reading of a larger Asian effective size and recent contraction elsewhere.
- Dufresnes and colleagues (2017), PLoS ONE 12: e0170522: positive inbreeding coefficients in hemp varieties and the suggestion of breeding bottlenecks; clonal propagation and the discarding of males in drug-type breeding.
- Sawler and colleagues (2015), PLoS ONE 10: e0133292: cannabis as wind-pollinated, dioecious and highly heterozygous.
- Welling and colleagues (2016), Frontiers in Plant Science 7: 1113: the difficulty of regenerating a wind-pollinated, dioecious crop; isolation distances of up to 5 km; drift attributed to regeneration in other crops; the limits of pollen-secure facilities; seed cryopreservation.
- Lemeshev, Rumyantseva and Clarke (1994), Journal of the International Hemp Association 1: 3–5: the Vavilov Institute collection in 1993; seed viability of about five years; the 1,000-plant minimum; the 1993 regrowings and their plant numbers, station by station.
- Clarke (1998), Journal of the International Hemp Association 5: 75–79: the five-year results of the regeneration programme; accessions multiplied from few seeds.
Terms
- Drift here is random genetic drift. Felsenstein keeps the word "random" to separate it from the physicists' "drift", which names a force with a direction.
- Regrowing, regeneration and reproduction all name the growing of a stored seed accession to obtain fresh seed. The reports of the Vavilov Institute programme call it reproduction; Welling and colleagues call it regeneration.
- The founder effect and a population bottleneck are both reductions in the number of individuals that pass genes on: the first when a few found a new population, the second when an existing population shrinks.
Source discrepancies
- Seed life at the Vavilov Institute. The report on 1993 gives about five years under normal storage before hemp seed loses viability. The report on 1994 gives three to four years before germination falls below 80 per cent, citing Khoroshailov and Zhukova (1978).
- What the New York cluster shows. Aina and colleagues attribute its low heterozygosity to small population size and geographic isolation, as a possibility; they do not name drift for that cluster. Their suggestion of local drift concerns populations near Hardy–Weinberg equilibrium in general.