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categories: ["genetics", "society"]categories: ["genetics", "society"]tags: ["crispr", "malaria", "ecology", "biosafety", "governance", "mosquitoes"]tags: ["crispr", "malaria", "ecology", "biosafety", "governance", "mosquitoes"]summary: "Genetic elements engineered to bias their own inheritance above the Mendelian half, allowing an introduced trait to spread through a wild population."summary: "Genetic elements engineered to bias their own inheritance above the Mendelian half, allowing an introduced trait to spread through a wild population."updated: "2026-08-23"updated: "2026-10-29"humanEvidence: "No drive-carrying organism has been released anywhere as of 2026, so the human outcome claimed for the technology, reduced malaria transmission, is untested; every suppression result comes from caged mosquito populations."humanEvidence: "No drive-carrying organism has been released anywhere as of 2026, so the human outcome claimed for the technology, reduced malaria transmission, is untested; every suppression result comes from caged mosquito populations."access: "Nothing to obtain: drives exist only in contained laboratory and cage colonies, and no regulator anywhere has authorised a field release."access: "Nothing to obtain: drives exist only in contained laboratory and cage colonies, and no regulator anywhere has authorised a field release."reversibility: "irreversible"reversibility: "irreversible"lines 21–27 → 21–276 unchanged lines not shown
"rows": [ "rows": [ { "label": "Type", "value": "Super-Mendelian inheritance element" }, { "label": "Type", "value": "Super-Mendelian inheritance element" }, { "label": "Proposed", "value": "2003 (Austin Burt)" }, { "label": "Proposed", "value": "2003 (Austin Burt)" }, { "label": "CRISPR version", "value": "2014–2015" }, { "label": "CRISPR version", "value": "2014-2015" }, { "label": "Leading target", "value": "Malaria mosquitoes" }, { "label": "Leading target", "value": "Malaria mosquitoes" }, { "label": "Field release", "value": "None as of 2026" }, { "label": "Field release", "value": "None as of 2026" }, { "label": "Governance forum", "value": "Convention on Biological Diversity" }, { "label": "Governance forum", "value": "Convention on Biological Diversity" },lines 36–49 → 36–498 unchanged lines not shown
A standard homing drive consists of a nuclease, a guide RNA that specifies a site in the host genome, and the whole cassette inserted at that same site. In a heterozygote, the drive-bearing chromosome expresses the nuclease, which cuts the corresponding site on the intact homologous chromosome. If the cell repairs that break by homologous recombination, it uses the drive-bearing chromosome as template and copies the entire cassette across. The organism, formerly heterozygous, is now homozygous, and every gamete carries the drive.A standard homing drive consists of a nuclease, a guide RNA that specifies a site in the host genome, and the whole cassette inserted at that same site. In a heterozygote, the drive-bearing chromosome expresses the nuclease, which cuts the corresponding site on the intact homologous chromosome. If the cell repairs that break by homologous recombination, it uses the drive-bearing chromosome as template and copies the entire cassette across. The organism, formerly heterozygous, is now homozygous, and every gamete carries the drive. The two useful designs differ in what they carry. **Population modification** drives spread a cargo that makes the organism harmless — in mosquitoes, an effector that blocks development of the malaria parasite — while leaving the population intact. **Population suppression** drives target a gene required for female fertility or sex determination; the drive spreads while it is rare and heterozygous, and the population collapses as homozygotes accumulate. Suppression is more powerful and less reversible.The two useful designs differ in what they carry. **Population modification** drives spread a cargo that makes the organism harmless (in mosquitoes, an effector that blocks development of the malaria parasite) while leaving the population intact. **Population suppression** drives target a gene required for female fertility or sex determination; the drive spreads while it is rare and heterozygous, and the population collapses as homozygotes accumulate. Suppression is more powerful and less reversible. > [!key] Why anyone is attempting this> [!key] Why anyone is attempting this> Malaria kills roughly six hundred thousand people a year, most of them African children under five, and insecticide resistance has eroded the effectiveness of bed nets and spraying.[^who2024] A drive is one of very few proposals that would not require sustained delivery of anything to the households at risk.> Malaria kills roughly six hundred thousand people a year, most of them African children under five, and insecticide resistance has eroded the effectiveness of bed nets and spraying.[^who2024] A drive is one of very few proposals that would not require sustained delivery of anything to the households at risk. ## Development history## Development history The concept was worked out in theory a decade before anyone could build one, and the decisive change was not an insight about population genetics but the arrival of a nuclease that could be aimed at an arbitrary sequence.The concept was worked out in theory a decade before anyone could build one, and the decisive change came from a nuclease that could be aimed at an arbitrary sequence rather than from any new insight about population genetics. ```timeline```timeline[[lines 58–68 → 58–688 unchanged lines not shown
The technical arc has been consistent: drives work in insects, resistance is the main obstacle, and careful target choice can defeat resistance in a cage. The unresolved questions are all about what happens outside one.The technical arc has been consistent: drives work in insects, resistance is the main obstacle, and careful target choice can defeat resistance in a cage. The unresolved questions are all about what happens outside one. One feature of the field's history is unusual. The 2014 paper by Kevin Esvelt, [[george-church]] and colleagues that described CRISPR drives also argued for containment standards and public discussion before any drive was built, and was published alongside a policy piece to that effect. The technology was therefore proposed and criticised by the same people at the same time, an inversion of the sequence at the [[asilomar-conference]] four decades earlier, where the moratorium followed the capability.The field's history has an unusual feature. The 2014 paper by Kevin Esvelt, [[george-church]] and colleagues that described CRISPR drives also argued for containment standards and public discussion before any drive was built, and was published alongside a policy piece to that effect. The technology was therefore proposed and criticised by the same people at the same time, an inversion of the sequence at the [[asilomar-conference]] four decades earlier, where the moratorium followed the capability. ## Resistance## Resistance The drive's own mechanism generates its principal failure mode. When the nuclease cuts the homologous chromosome, homologous recombination copies the drive across, but end joining instead produces a small insertion or deletion at the cut site. That altered sequence is no longer recognised by the guide RNA. If the resulting allele still works, it is a resistance allele that is immune to the drive and favoured by selection whenever the drive imposes a fitness cost — and suppression drives impose a very large one.The drive's own mechanism generates its principal failure mode. When the nuclease cuts the homologous chromosome, homologous recombination copies the drive across, but end joining instead produces a small insertion or deletion at the cut site. That altered sequence is no longer recognised by the guide RNA. If the resulting allele still works, it is a resistance allele that is immune to the drive and favoured by selection whenever the drive imposes a fitness cost, and suppression drives impose a very large one. Two countermeasures have worked in the laboratory. One is to target a sequence so functionally constrained that almost any indel destroys the gene, so resistance alleles are themselves lethal or sterile. The other is multiplexing several guide RNAs against the same gene, so that resistance requires simultaneous escape at multiple sites. Neither has been tested against the standing genetic variation of a wild population, which is far larger than any cage contains.Two countermeasures have worked in the laboratory. One is to target a sequence so functionally constrained that almost any indel destroys the gene, so resistance alleles are themselves lethal or sterile. The other is multiplexing several guide RNAs against the same gene, so that resistance requires simultaneous escape at multiple sites. Neither has been tested against the standing genetic variation of a wild population, which is far larger than any cage contains. lines 83–102 → 83–10214 unchanged lines not shown
Because a standard homing drive is designed to spread indefinitely, most current research effort goes into designs that do not.Because a standard homing drive is designed to spread indefinitely, most current research effort goes into designs that do not. - **Split drives** separate the nuclease from the guide RNA, so the element spreads only where the missing component has been supplied — usually only in a laboratory strain.- **Split drives** separate the nuclease from the guide RNA, so the element spreads only where the missing component has been supplied, usually only in a laboratory strain.- **Daisy-chain drives** arrange elements in a series in which each drives the next; the chain is consumed from one end, and the drive exhausts itself after a predictable number of generations.[^noble2019]- **Daisy-chain drives** arrange elements in a series in which each drives the next; the chain is consumed from one end, and the drive exhausts itself after a predictable number of generations.[^noble2019]- **Threshold-dependent designs** spread only if released above a frequency high enough that they cannot cross into a neighbouring population by ordinary migration.- **Threshold-dependent designs** spread only if released above a frequency high enough that they cannot cross into a neighbouring population by ordinary migration.- **Reversal drives** are intended to overwrite a released drive with a neutral sequence. They restore function but do not restore the original sequence, and no field demonstration exists.- **Reversal drives** are intended to overwrite a released drive with a neutral sequence. They restore function but do not restore the original sequence, and no field demonstration exists. The logic parallels the synthetic auxotrophy used for biocontainment in [[recoded-organisms]]: rather than trusting physical barriers, the organism is engineered so that escape is self-defeating. The honest position is that reversibility here is a design intention rather than a demonstrated capability. Nothing engineered has yet been recalled from a wild population.The logic parallels the synthetic auxotrophy used for biocontainment in [[recoded-organisms]]: rather than trusting physical barriers, the organism is engineered so that escape is self-defeating. Reversibility here is a design intention rather than a demonstrated capability. Nothing engineered has yet been recalled from a wild population. ## Risks and governance## Risks and governance The ecological concerns are of three kinds: effects on species that eat or are pollinated by the target; spread of the construct into related species through hybridisation, which is a live issue in the *Anopheles gambiae* species complex; and the possibility that a suppression drive succeeds more completely or more widely than intended. The [[crispr-off-target-effects|off-target problem]] takes an unusual form here, since a drive amplifies itself over generations and any unintended edit it carries travels with it.The ecological concerns are of three kinds: effects on species that eat or are pollinated by the target; spread of the construct into related species through hybridisation, which is a live issue in the *Anopheles gambiae* species complex; and the possibility that a suppression drive succeeds more completely or more widely than intended. The [[crispr-off-target-effects|off-target problem]] takes an unusual form here, since a drive amplifies itself over generations and any unintended edit it carries travels with it. Governance has settled into an uneasy pattern. A 2016 United States National Academies report endorsed continued research with staged testing rather than prohibition. Proposals for a global moratorium at the Convention on Biological Diversity were rejected in 2018 in favour of decisions calling for case-by-case risk assessment and for the free, prior and informed consent of indigenous peoples and local communities potentially affected. The World Health Organization has published a testing framework for genetically modified mosquitoes. None of these instruments is binding in the way that domestic biosafety law is, and a drive released anywhere will not respect the jurisdiction that authorised it — a structural problem shared with the concerns raised in [[mirror-life]] and, more distantly, in [[dual-use-research]].Governance has settled into an uneasy pattern. A 2016 United States National Academies report endorsed continued research with staged testing rather than prohibition. Proposals for a global moratorium at the Convention on Biological Diversity were rejected in 2018 in favour of decisions calling for case-by-case risk assessment and for the free, prior and informed consent of indigenous peoples and local communities potentially affected. The World Health Organization has published a testing framework for genetically modified mosquitoes. None of these instruments is binding in the way that domestic biosafety law is, and a drive released anywhere will not respect the jurisdiction that authorised it, a structural problem shared with the concerns raised in [[mirror-life]] and, more distantly, in [[dual-use-research]]. The consent question has no clean answer. The population that must agree to a release is not the population that will be affected, since mosquitoes cross borders and generations — a problem formally similar to the objection that no future person can consent to [[germline-editing]], but at ecosystem scale. Frameworks developed for [[governance-of-genome-editing]] in medicine assume an identifiable patient and do not transfer, and arguments from the [[precautionary-principle]] cut both ways when the status quo is a disease that kills hundreds of thousands of people annually. Drives are also a standard case in the [[existential-risk]] literature, less because a mosquito drive threatens humanity than because it is the first cheap technology whose intended behaviour is unbounded spread. Proposals for staged, reversible deployment are the clearest applied instance of [[differential-technological-development]] in biology.The consent question has no clean answer. The population that must agree to a release is not the population that will be affected, since mosquitoes cross borders and generations, a problem formally similar to the objection that no future person can consent to [[germline-editing]], but at ecosystem scale. Frameworks developed for [[governance-of-genome-editing]] in medicine assume an identifiable patient and do not transfer, and arguments from the [[precautionary-principle]] cut both ways when the status quo is a disease that kills hundreds of thousands of people annually. Drives are also a standard case in the [[existential-risk]] literature, less because a mosquito drive threatens humanity than because it is the first cheap technology whose intended behaviour is unbounded spread. Proposals for staged, reversible deployment are the clearest applied instance of [[differential-technological-development]] in biology. ## Outlook## Outlook removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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