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What happens when a piece of the lac operon breaks? In this video, we'll describe the must-know lac operon mutations and their impacts on gene expression, including the super repressor and constitutive operator mutations. We'll also work some examples with partial diploids to highlight the different effects of cis-acting and trans-acting mutations, and discuss how to determine whether a mutation is dominant or recessive. #lacoperonmutations #superrepressor #constitutiveoperator This is part 3 of a lac operon miniseries. You may also want to check out… Part 1: *The lac operon structure and function:* https://youtu.be/U9c4V0BKuaQ Part 2: *Glucose and lac operon expression:* https://youtu.be/rw5-pY1BB90 IN THIS VIDEO: 00:52: Lac operon mutations notation 01:04: *Wild-type alleles vs null mutations* 01:36: Mutations in lac operon structural genes 03:02: *Non-inducible* lac operon mutations (P- and super repressor) 04:51: *Constitutive* lac mutations (I- and constitutive operator) 06:13 Lac Operon *Partial diploids (merozygotes)* 07:10 *Examples* of lac operon partial diploid mutations 08:27: *Cis-acting mutations* impact the sequence they're found on 10:27: *Trans-acting mutations* can impact all copies of lac operon 13:19: Tips for working problems with lac operon mutations New videos are always on the way - subscribe so you don't miss any of my biology tips :) Connect with me! Website: http://www.yourotherbioprof.com Instagram: instagram.com/yourotherbioprof

You already know lactose is important for regulating the lac operon, but it's not the only sugar involved. Through *catabolite repression*, glucose also plays a key role. In this video, we'll look at different combinations of *lactose and glucose availability,* and how lac operon expression is impacted. You'll see how *CAP and cyclic AMP* can induce the highest levels of lac operon expression in the absence of glucose, and explain why expression is lower when glucose is around. And, you'll see why this is described as a *positive inducible* mechanism. #cataboliterepression #lacoperonglucose #lacoperoncyclicAMP This is part of a lac operon miniseries. You may also be interested in… *The lac Operon Structure and Function:* https://youtu.be/U9c4V0BKuaQ *Lac Operon Mutations:* https://youtu.be/st2nx97NmNk And, learn more about... *Upstream and Downstream on DNA:* https://youtu.be/XDKUL9JB66s *Positive, Negative, Inducible, Repressible Operons:* https://youtu.be/Qd16nt1WdAc 00:50: *Review the lac operon* 01:29: *Catabolite repression* 02:15: Compare and contrast: *lac repressor and CAP (CRP)* 03:39: Glucose and *cAMP* - inverse relationship 04:44: lac operon expression: *lactose but no glucose* 05:46: lacP is a weak promoter 07:01: lac operon expression: * both lactose and glucose* 08:17: lac operon expression: *no lactose and no glucose* 09:21: lac operon expression: *glucose but no lactose* 09:44: Catabolite repression is a *positive inducible* mechanism 11:01: *Summary table* of lac operon expression New videos are always on the way - subscribe so you don't miss any of my biology tips :) Connect with me! Website: http://www.yourotherbioprof.com Instagram: instagram.com/yourotherbioprof

Need to understand the basics of the E. Coli *lac operon*? Watch this video! Operons are studied as examples of how prokaryotes *regulate gene expression* at the level of transcription - and the lac operon is the classic example! We'll describe and label the *structure of the lac operon*, and see the role of the *lac repressor* in regulating expression of the lac operon depending on lactose availability. We'll explain why the lac operon is a *negative inducible operon*, and what it means to have “leaky” expression. Stay with me to the end to make the lac operon make sense! #lacoperon #lacrepressor #negativeinducibleoperon This is part of a lac operon miniseries. You may also be interested in… *The role of glucose in lac operon expression:* https://youtu.be/rw5-pY1BB90 *Lac Operon Mutations:* https://youtu.be/st2nx97NmNk Want to learn more? *Upstream and Downstream on DNA:* https://youtu.be/XDKUL9JB66s *Positive, Negative, Inducible, Repressible Operons:* https://youtu.be/Qd16nt1WdAc 01:05: Lac operon structure 01:34: Lac operon *structural genes* 03:48: Lac operon with no lactose 04:22: lacI and the *lac repressor* 05:47: Lac operon when lactose is available 07:24: Inducer: *allolactose* vs lactose 09:13: Lac operon is *negative inducible* 10:15: *"Leaky" expression* of the lac operon New videos are always on the way - subscribe so you don't miss any of my biology tips :) Connect with me! Website: http://www.yourotherbioprof.com Instagram: instagram.com/yourotherbioprof

When do mom's genes override yours? When it's a *genetic maternal effect!* In this video, we'll see how the maternal genotype can determine an offspring's phenotype, regardless of what the offspring's own alleles say. We'll use snail shell coiling as an example of genetic maternal effect to see how maternal effect genes shape an offspring's phenotype early in development. And we'll briefly highlight how genetic maternal effect is different from cytoplasmic inheritance (even though mom is definitely important in that one, too!)... #geneticmaternaleffect #maternaleffect #snailshellcoiling 00:13 What is *genetic maternal effect?* 00:46 *Maternal effect genes* 01:46 Example of genetic maternal effect: *snail shell coiling* (dextral or sinistral) 05:14 Genetic maternal effect vs cytoplasmic inheritance Related videos: Genotype vs phenotype: https://youtu.be/XhwPr3Yxazg Why are some alleles dominant or recessive?: https://youtu.be/7DmaUO-BNFM New videos are always on the way - subscribe so you don't miss any of my biology tips :) Connect with me! Website: http://www.yourotherbioprof.com Instagram: instagram.com/yourotherbioprof

Still a little unsure about *lethal alleles?* In this video, we'll define lethal alleles, and explain the difference between *recessive lethal* and *dominant lethal* alleles. We'll use the "agouti" gene for mouse coat color with the *recessive lethal "yellow" allele* to show how crosses involving lethal alleles can lead to unexpected offspring ratios. #lethalallele #recessivelethal #dominantlethal 00:11 What is a lethal allele? 00:37 What is a recessive lethal allele? 01:11 Example of a recessive lethal allele - agouti gene and yellow allele for mouse coat color 01:52 Why a 2:1 offspring ratio from crossing yellow mice? 03:24 Pleiotropy 03:46 What is a dominant lethal allele? Why are dominant lethal alleles less common in populations than recessive lethal alleles? 04:20 Example of a dominant lethal allele - Huntington's disease *Want to learn more? Try these related videos:* Why are some Alleles Dominant (or Recessive)?: https://youtu.be/7DmaUO-BNFM Multiple Alleles: https://youtu.be/_E03XqaQUL4 Penetrance and Expressivity: https://youtu.be/_6a6LlSSH6E New videos are always on the way - subscribe so you don't miss any of my biology tips :) Connect with me! Website: http://www.yourotherbioprof.com Instagram: instagram.com/yourotherbioprof

Let's learn about penetrance and expressivity, and see how those important genetics concepts can make for unexpected phenotypes. Examples of incomplete penetrance and variable expressivity show how genotype and phenotype aren't always a match. #penetrance #expressivity #incompletepenetrance #completepenetrance #variableexpressivity 0:16 What is *Penetrance*? Example of *Complete Penetrance* (Full Penetrance) 0:54 Example of *Incomplete Penetrance* (Reduced Penetrance) 2:02 Penetrance of Huntington's Disease alleles 3:15 What is *Expressivity*? 3:34 Example of *Constant Expressivity* (Narrow Expressivity) 3:55 Example of *Variable Expressivity* (Broad Expressivity) 4:38 Polydactyly shows incomplete penetrance and variable expressivity 5:08 Why incomplete penetrance and variable expressivity? 5:44 *Review penetrance and expressivity* Want to learn more? Try these related videos: Genotype and Phenotype Explained: https://youtu.be/XhwPr3Yxazg Why are some Alleles Dominant (or Recessive)?: https://youtu.be/7DmaUO-BNFM New videos are always on the way - subscribe so you don't miss any of my biology tips :) Connect with me! Website: http://www.yourotherbioprof.com Instagram: instagram.com/yourotherbioprof [note: this video is a re-upload to correct a glitchy animation in the original version!]

Why is the trp operon negative repressible? How does attenuation stop transcription of the trp operon? How do bacteria turn genes off? The tryptophan operon ("trp operon") in E. coli has two key regulatory mechanisms - let's look at both! The trp operon is regulated by a *negative repressible* mechanism, and by *attenuation,* where translation (the position of the ribosome) actually impacts transcription! *When tryptophan concentration in the cell is low*, the cell wants to keep transcription of the trp operon ON - to make the instructions to build more enzymes to make more tryptophan. The trp repressor stays out of the way, allowing RNA polymerase to start transcription. Translation of that mRNA starts, too! The low trp levels mean tRNAs charged with tryptophan are hard to find, so the ribosome stalls, waiting for a tryptophan delivery. An *antitermination hairpin* forms, and RNA polymerase keeps moving along... *When tryptophan concentration in the cell is high*, the trp repressor binds excess tryptophan, causing a conformational change in the trp repressor. This allows the repressor to *bind the operator - blocking RNA polymerase* from initiating transcription. But the repressor isn't perfect - it can fall off the operator prematurely, allowing transcription to begin (even though it's not needed). Thanks to plenty of trp-charged tRNAs, the ribosome moves quickly, causing formation of a *termination hairpin*, and stopping this unneeded transcription. #repressor #attenuation #trpoperon *Operons: Positive, Negative, Inducible, Repressible:* https://youtu.be/Qd16nt1WdAc *What does Upstream Mean on DNA and RNA?:* https://youtu.be/XDKUL9JB66s 00:32 Structure of the trp operon 01:40 Trp operon with low tryptophan concentration 02:39 Trp operon with high concentration of tryptophan 03:18 The trp operon is a negative repressible operon 04:01 Trp leader region (trpL) and hairpins 05:09 Transcription and translation happen in the same place in prokaryotes 05:39 trpL mRNA has tryptophan codons 05:58 Attenuation of transcription (termination hairpin) 06:49 Antitermination hairpin with low trp concentration 07:32 Summary of attenuation trp operon 08:20 Attenuation of operons that produce amino acids 08:45 Why attenuation of trp operon? 09:16 Summary of trp operon regulation New videos are always on the way - subscribe so you don't miss any of my biology tips :) Connect with me! Website: http://www.yourotherbioprof.com Instagram: instagram.com/yourotherbioprof

A quick explanation of negative inducible operons. Key vocabulary: negative regulation, repressor, operator, inducible, inducer New videos are always on the way - subscribe so you don't miss any of my biology tips :) Ready to learn more? *Positive, Negative, Inducible, Repressible Operons:* https://youtu.be/Qd16nt1WdAc Connect with me! Website: http://www.yourotherbioprof.com Instagram: instagram.com/yourotherbioprof