Talk:Inbred line

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Page scope

Inbred line covers inbred lines as a genetic object: how a line approaches homozygosity under selfing and under mating of full siblings, fixation of different alleles in different lines, residual heterozygosity, the ways inbred lines of cannabis are made (sex reversion, isolators for monoecious hemp, single-seed descent, doubled haploids), their use as parents of hybrids and in genome research, and the label IBL in the seed trade. Heterozygosity as a measure belongs to Heterozygosity. The cannabis breeding system, feminised seed and the studies of inbreeding depression after selfing belong to Outcrossing. Hybrid vigour belongs to Heterosis, hybrid seed to F1 hybrid, the fitness consequences of inbreeding to Inbreeding depression and the recessive characters seen in inbred hemp to Dominance and recessivity.

Data verification

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Discussion

Sources

Felsenstein (2019), Theoretical Evolutionary Genetics: selfing and the inbreeding coefficient, with the proportions of self-fertilising lines of each genotype over seven generations (pp. 231–233); full-sib mating (p. 237); isolated inbred lines and crossing them (pp. 242–244); loss of heterozygosity by drift (pp. 254–256); inbreeding depression and selection during inbreeding, and the means of crosses between inbred lines (pp. 411–414).
Serkov and Klimova (2016), Niva Povolzh'ya 2 (39): 52–60 (in Russian): self-pollinated lines of monoecious hemp bred at the Penza Research Institute of Agriculture from 2006, with a review of earlier Soviet work on inbreeding in hemp.
Barcaccia and colleagues (2020), Frontiers in Plant Science 11: 573299: inbred lines by selfing and full-sib mating; the breeding of Skunk No. 1; true and pseudo-F₁ hybrids; combining ability, diallel tests and multi-way hybrids; markers for the homozygosity of lines.
Galán-Ávila and colleagues (2021), Frontiers in Plant Science 12: 669424: cold pretreatment of male flower buds and the first induction of androgenesis in cannabis.
Grassa and colleagues (2021), New Phytologist 230: 1665–1679: the Skunk No. 1 and Carmen parents of the mapping population, sib-crossed for five generations; the highly inbred CBDRx (cs10) genome; residual heterozygosity in CBDRx, FL18 and FL49.
De Meijer and colleagues (2003), Genetics 163: 335–346: crosses between inbred plants of pure CBD and pure THC chemotype.
Lynch and colleagues (2025), Nature 643: 1001–1010: EH23, an F₁ of the female inbred lines ERB and HO40, its haplotype-resolved assemblies and F₂.
Stack and colleagues (2025), International Journal of Molecular Sciences 26: 1165: runs of homozygosity in seven genome assemblies, among them the inbred line FL 58.
García-de Heer and colleagues (2026), Horticulture Research 13: uhag038: single-seed descent with sex reversion in 16 accessions; heterozygosity at 1,500 SNPs; abnormal flowers and failure rates by sex; five F₁ hybrids from sixth-generation lines.
The Hemp Depot listing of ATAO Genetics' Mazar-I-Shariff IBL F5, for the seed-trade use of the label.

Where the sources disagree

Doubled haploids. Galán-Ávila and colleagues (2021) obtained only multinucleate structures that did not develop further, and García-de Heer and colleagues (2026) write that methods of inducing doubled haploids have so far been unsuccessful in cannabis. A preprint posted on bioRxiv in October 2024 (Tonolo, doi:10.1101/2024.10.25.620185), not peer-reviewed, reports doubled-haploid regenerants of drug-type cannabis from microspore callus, confirmed as homozygous at 12 SNP markers.
Seed yield of the hybrids. The abstract of García-de Heer and colleagues gives the rise in seed yield of the F₁ hybrids, 3.9 to 155 per cent, against their midparents; the results section gives the same range against their midancestors, the original open-pollinated lines.
Timing of the inbreeding. The same study gives up to six rounds of single-seed descent "in an 18-month period" in its abstract, and rounds completed between April 2021 and October 2023 in its results.

Terms

Inbred line (IBL in García-de Heer and colleagues and in the seed trade): a line bred by repeated mating of close relatives until it is nearly homozygous. In the seed trade the label is also used for lines kept by open pollination within the line.
Single-seed descent: carrying a line forward from one plant in each generation, by selfing.
S₁, S₂ … S₆: the first, second and later generations of selfing.
Functional homozygosity: in García-de Heer and colleagues, heterozygosity below 3 per cent at their 1,500 SNPs.
Sex reversion: the induction of flowers of the other sex, male flowers on a female plant with silver thiosulfate or female flowers on a male plant with ethephon.
General and specific combining ability: the average performance of a line in hybrid combinations, and the performance of one particular cross beyond that average.
Ordinary male plants (Russian обычная посконь): dioecious-type male plants appearing in a monoecious hemp population.

Further figures from the sources

In the lines of Serkov and Klimova, the mean THC content rose from 0.029 per cent in the first selfed generation to 0.062 per cent in the fifth, with ranges as wide as 0.004 to 0.514 per cent. The total content of the main cannabinoids followed the weather of the year: 0.449 per cent on average in the most favourable season, 0.814 per cent in a dry one and 1.310 per cent in an extremely dry one.
The share of heterozygotes falling from 100 per cent to 1.5625 per cent over six generations is the plan of the Russian programme for a single pair of alleles, not a measured value.

Images reserved in the article

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

File:Cannabis-inbred-lines-fixation-under-selfing.jpg (From a population to inbred lines), a chart to be drawn: one stacked bar for each generation from 0 to 7, divided into the shares of self-fertilising lines that are AA, Aa and aa when the base population has allele frequencies of 0.6 and 0.4 and is in Hardy–Weinberg proportions: 0.36, 0.48 and 0.16 at generation 0, then 0.48, 0.24, 0.28; 0.54, 0.12, 0.34; 0.57, 0.06, 0.37; 0.585, 0.03, 0.385; 0.5925, 0.015, 0.3925; 0.59625, 0.0075, 0.39625; and 0.598125, 0.00375, 0.398125 at generation 7. No crop or study names.