--- title: "Plasmids, Mobile Elements and How Resistance Spreads" description: "Resistance genes can occur on chromosomes, plasmids and transposons. Transposons can move genes between DNA locations, while transferable plasmids can carry several resistance genes between cells. Res" canonical: https://lightmysky.com/learn/science/plasmids-mobile-elements-and-how-resistance-spreads-mt_Vk0qOY64qv source: https://lightmysky.com/learn/science/plasmids-mobile-elements-and-how-resistance-spreads-mt_Vk0qOY64qv.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Plasmids, Mobile Elements and How Resistance Spreads Resistance genes can occur on chromosomes, plasmids and transposons. Transposons can move genes between DNA locations, while transferable plasmids can carry several resistance genes between cells. Resistance spreads through both bacterial reproduction and horizontal transfer. Subject: Science · Area: Microbiology · Ages 20 to 21 Page: https://lightmysky.com/learn/science/plasmids-mobile-elements-and-how-resistance-spreads-mt_Vk0qOY64qv ## Ready when they can - Explains why a plasmid can be gained and lost while the chromosome stays the same. - Uses genetic evidence to explain how one mobile element can deliver several resistance genes together. - Predicts how plasmid costs, benefits, loss and transfer affect carrier frequency after a selecting drug is withdrawn. ## Lesson: Resistance travels as luggage A plasmid is DNA that can replicate separately from the chromosome, using the cell's machinery. It can be gained by transfer or lost when a daughter fails to inherit it, even if the chromosome is unchanged. Many plasmids carry extra traits, such as drug resistance. Resistance genes can also be chromosomal. Their location must be measured, not inferred from the resistance trait alone. The previous topic called direct donor-recipient DNA transfer conjugation. Some plasmids can use this route, but not all plasmids can transfer themselves. A transposon is a DNA segment that can change location within DNA or move between DNA molecules. It can move from a chromosome to a plasmid inside one cell. That is transposition. Transfer to another cell is a separate event. One plasmid can carry several resistance genes. If a transferred copy arrives and those genes function in the recipient, several resistance traits can appear together. For example, an intact plasmid carrying resistance genes A and B can be favored by drug A, retaining the linked B gene too. This is co-selection. Joint resistance alone does not prove shared plasmid cargo; DNA evidence is needed. *(drawing: A and B name resistance genes in this example. One plasmid transfer delivers both genes; resistance also requires them to function.)* A drug can favor cells with a plasmid that protects against it. After withdrawal, frequency may fall if the plasmid slows growth, has no other benefit, is sometimes lost and does not transfer. Withdrawal alone does not guarantee decline. Low cost, other benefits or continued transfer may maintain carriers. Resistant cells also spread by reproduction and transmission, so investigations may need both cell and plasmid histories. **Recap.** Separate transposition from transfer between cells. Linked genes can travel together; plasmid persistence depends on costs, benefits, loss and transfer. *Lesson explanations, questions and study cards were written for this dataset, with scientific background from Microbiology.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Horizontal Gene Transfer: Uptake, Contact and Delivery](https://lightmysky.com/learn/science/horizontal-gene-transfer-uptake-contact-and-delivery-mt_mrmn0_nQf7) ## Opens up - [CRISPR: A Bacterial Defence Turned into a Tool](https://lightmysky.com/learn/science/crispr-a-bacterial-defence-turned-into-a-tool-mt_0joPWRvOLw)