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Joseph Merritt Ramsey
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This 11 page Class Notes was uploaded by Joseph Merritt Ramsey on Monday January 25, 2016. The Class Notes belongs to CELL 2050 at Tulane University taught by Dr. Meenakshi Vijayaraghavan in Winter 2016. Since its upload, it has received 87 views. For similar materials see Genetics in Science at Tulane University.
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Date Created: 01/25/16
January 20 2O 16 Chapter 4 Extensions of Mendelian Genetics 0 Limitations of Mendel s Work 0 Modern Genetics Begins to Ask Why 0 So how do other mutations manifest themselves other than the simple above potential mechanisms I 1 Gain of Function I 2 Dominant Negative 3 Haploinsufficiency 0 Generally genes are transcribed and proteins created by a combination of each allele on the chromosomes 0 Ex Consider a deletion o In essence one is note enough the Haplo is not enough to express 0 Thinks of it this way 0 A gene will be expressed with 50 Units of protein X created 0 You have two alleles that are both wild type one is just highly expressive varies per person 0 In the highly expressive each allele codes for 50 units so it is Haplo sufficient 0 But in the low expressive each is only 30 haploinsufficient 0 Diagram 0 Looking Dominance o 1 Simple Dominance 3 l I Straightforward Mendelian Expectations with the 31 Raito o 2 Incomplete Dominance 12 1 I One copy of the dominant allele is not enough to express the gene I Ex 4 O clock Flower o A mix occurs Punnett Square View Diagram I Ex A Molecular Look at the Pea Shape Take a look at protein composition and it becomes clear that the Homozygous Dominant varies from the Heterozygous Looking at the EET Gene Expression But must be done molecularly speaking I Ex PKU Phenylketonuria Molecular Perspective Same idea here PKU patients lack the functioning protein Phenylalanine Hydroxilase o This breaks down Phenylalanine 0 Without it Phenylalanine releases damaging ketones So blood samples can be taken and checked for Phenylalanine composition re ective of its proper breakdown 0 Healthy Homozygous lmgdL 0 Carrier Heterozygous 2 3mgdL o Infected Homozygous Recessive 6 8mgdL o 3 Incomplete Penetrance Varies by Generation I Normally the genotype penetrates the phenotype in order to express the present gene The dominant trait is said to have the ability to penetrate the phenotype But when the dominant trait is present but somehow unexpressed it is known as incomplete penetrance I Important to note the different between Penetrance and Expressivity Penetrance viewed in the population the capacity to be expressed in Heterozygous individuals 0 Only consider Heterozygotes because the other two are easy to identify and explain already 0 So within a population the gene has 66 penetrance Expressivity deals with an individual how is the gene expressed In the example below the consistent lack of expression of the dominant allele is penetrance while one person having 12 and another having 11 is expressivity I Ex Polydactism Being a heterozygote with the Dominant Polydactyl o This allows for the trait to skip generations with relative ease I Possible Explanations o 1 Environmental environmental factors in uence the gene expression 0 1 Light I Snapdragon present different colors depending on what temperature it is in which they grow 0 11 Temperature I Drosophilia facets are more present when growing in cold weather and less so in warm weather 0 III Diet I PKU patients cannot have Phenylalanine in their diet but strict regulations allow them to live perfectly fine I Can they be reversed o A question may be however if they don t catch it early can it be reversed o PKU doesn t present such a prospect but the conditioned allele on Shibiar alleles can be 0 Flies grown at given temperatures can have the effects reversed o 2 Modifier Genes o 3 Combination of the First Two 0 4 Overdominance 12 1 But Heterozygotes are Selected for I Overdominance deals with Heterozygous individuals only looking at the carriers and only looking at one gene 0 These Carriers have an advantage I Ex Sickle Cell 0 Hemoglobin overview 0 Made up of four subunits Two Alpha Two Beta 0 A small point mutation occurs on the Alpha I GAG goes to GTG on the DNA I Goes from Glycine charged AA to Valine Neutral AA 0 Pressure then results in cytoskeletal transformation due to the neutral Valine connection I l Stiffness occurs because the cytoskeleton is inefficient leads to clotting I 2 They morphed form leads to inefficient Oxygen transport 0 Cells of Sickle Cell Lifespan 0 Each cell normally lives 90 120 but sickle cell cells only survive 10 20 0 So the body can t keep up 0 But Carriers have an advantage 0 HbA and HbS are the alleles 0 Their cells are mostly fine and properly functioning but a few of them present some sickle traits 0 When their cells are attacked by Malaria plasmodium propagation cannot occur I 1 They burst because of the shape I 2 They have a particular antigen from the trait expression 0 But non malarial environments don t have high heterozygote populations I Ex Tay Sachs o A mutation occurs in a lipid storage and synthesis protein 0 Allow them to fight TB I Ex PKU Females o In certain areas the likelihood to ingest the Ochratoxin A is much higher 0 Normally even a small ingestion is enough to cause a likely miscarriage but is not fatal to the mother 0 But PKU females do not experience such miscarriages I Why does Overdominance Occur o 1 Cellular Morphology o Antigen is present because of the slight expression Sickle Cell example 0 2 Dimerization of the Protein 0 Dimerization occurs to form the final protein Quartneary structure I 2 units come together 0 With another type of allele three possible dimerization possibilities arise I With two of the same allele only one permutation exists I Results in the creation of different Monodimers and Heterodimers 0 New capacities are created 0 3 Protein Reactivity 0 Say one allele reacts at a given temp low and another at a different temp high I With both present the organism can respond to low and high temperatures 0 So a range of enzyme activity is created I That range creates a survival advantage 0 5 Heterosis I This example begins to look at multiple genes Multiple genes are introduced so the genetic bene ts are not from an allelic mixture of a given gene they are from a conglomeration of genetic effects from multiple genes I Ex Crops Genes are introduced to optimize crop life I The phrase here is Hybrid Vigor Merely referring to the mix of alleles 0 Considering Multiple Alleles 0 Overview I Several mutations exist for a given gene each showing a slightly different and altered phenotype I Morphologies l Monomorphic one wild type exists 2 Polymorphic multiple wild types exist 3 Multiple Alleles o Polymorphism Only deals with One Gene I Hair and Eye Color may be a common consideration but consider how those manifest themselves They are a mix of genetic in uences in uenced by Polyploidy genes I A true example is blood type They are all the same gene and are not phenotypically affected by other genes But there are three different forms of the gene And if not force chooses for a particular phenotype it is Polymorphic But if the Wild type is chosen it is Monomorphic January 22 2O 16 Chapter 4 Extensions of Mendelian Genetics Continued 0 Limitations of Mendel s Work 0 Modern Genetics Begins to Ask Why 0 So how do other mutations manifest themselves other than the simple above potential mechanisms I 1 Gain of Function I 2 Dominant Negative I 3 Haploinsufficiency 0 Looking Dominance o 1 Simple Dominance 31 o 2 Incomplete Dominance 1 392391 o 3 Incomplete Penetrance Varies by Generation 0 4 Overdominance 1 392391 But Heterozygotes are Selected for o 5 Heterosis 0 Considering Multiple Alleles 0 Overview 0 Polymorphism Only deals with One Gene I Hair and Eye Color may I A true example is blood type 0 Monomorphism I The mutation distribution is not equal 0 Other alleles can exist but one wild type predominates so the phenotype is monomorphic o The mouse coat color is a good example 0 Agouti is dominant A 0 But the Black Yellow Body is possible at 0 And Black is also possible a 0 So in essence polymorphic alleles can be monomorphically expressed I Mouse Fur Example 0 This deals with pigmentation o Tyrosinase is responsible for pigmentation I Different Melanins can be acted upon I EuMelanin is a Dark Brown Black color I PheoMelanin is a Yellow Color 0 The gene for properly functioning Tyrosinase is C I So CC is complete Tyrosinase which Gives a lot of Eumelanin I Cc is a mix of Eumelanin and Pheomelanin which gives a grayish Agouti color I Then other recessive alleles exist 0 But there are Recesive alleles as well mutations that occurred on the tyrosine gene I cCh Chinchilla I ch Himalayan I c Albino 0 So Phenotypic expressions Can include I cChcCh Chinchilla I cchch Incomplete Dominance I cCh chc Paler Version of the other 0 As a side note these have interesting Thermolable properties specifically with the Himalayan variety I Body temperature in uences gene expression I The cold causes and increased expression when the Himalayan allele is present ch I This causes a darkening of the extremities 0 Examples of Multiple Alleles I Mouse Fur Color True Monomorphism o Mentioned above the distribution is not equal I Rabbit Fur Color Like Monomorphism but still all present 0 Detailed above I Lintels Like Monomorphism but still all present 0 Some predominate more than others but all alleles are still present Marbled 1 gt Marbled II gt Spotted Dotted They are equivalent gt Clear Dominate Form 1 Dominate Form 11 Strong Recessive Completely Recessive I Blood Types True Polymorphism 0 Different types of blood exist that are all equally as present 0 Conditional Alleles 0 Definition particular environmental conditions cause the gene expression I These alleles were mentioned in regards to the PKU discussion in Incomplete Penetrance I But unlike with penetrance reversal is much more difficult and or impossible purely environmental factors can often be reversed 0 Examples I Rabbits o Himalayan gene in rabbits 0 Tyrosine activation in the recessive Himalayan gene are in uenced by temperature upregulated in the cold I Siamese Cats 0 Same Tyrosine effects in the cold I Cattle 0 Cold now down regulated Tyrosine action for Cattle color I Drosophilia o Shibire genes regulating cytoskeletal development occurs normally at 210 or lower 0 Codominance 0 Definition I Multiple alleles present themselves as wild type dominate equal in phenotypic expression 0 Blood Types is a great View I The Blood Gene codes for Particular Antigens used for self recognition 0 i isoglutanogen mutant form lacks enzyme binding spot on the blood cell 0 A UDP Uridine DiPhosphate N Acetyl Galactosamine NAG binding site 0 B UDP Galactose G Binding Site I Glycosyltransferase Transfers sugars moves the sugar to the blood cell binding site I When exposed to the given blood types with sugar markers antibodies are generated because the host cell has no binding site for the foreign sugar eg 0 blood cell has no sites for A or B sugars I Blood Genotype Options 0 A IAIA or IAi o B IBIB or 113i 0 AB IAIB o O ii I Rhesus factor is the Rh factors for plasmid antigens I And M N blood types are for blood protein antigens I H Factor Bombay Blood Disorder 0 The HFactor generates the H Antigen which is the precursor to A and B antigens 0 So a mutation in the H Factor gene is detrimental to blood type because no A or B antigens exist 0 So no matter what the blood type is 0 no antigens o Cattle Color I Spots become present when Red Brown is crossed with White 0 Sex Linked Genes o Linked they are present on a Sex Chromosomes I Y Holandric Genes only about 83 present X About 500 present This phrase is generally used considering inheritance o Hemizygous Ex This term refers to the Y Chromosome One type of allele is present the idea behind homozygous but only one chromosome will carry that given allele whether on X or Y So the phrase is Hemizygous there s only one slot to fill Duchenne Dystrophy o Dystropin is a cytoskeletal protein that attached the cytoskeleton to the plasma membrane 0 So dysfunctional dystropin leads to inefficient muscle cell development 0 So the person has not development The disease affects men much more demonstrated by the reciprocal cross shows and X Linked Inheritance XD XD X01 X01 Xd XDXd XDXd XD XDXd XDXd XDY XDY XdY XdY Teeth Color 0 The enamel and coloration gene is located on the X Chromosome SeX Related Traits 0 Important Differences SeX In uenced o Refers to hormonal in uences on gene expression This is usually with Autosomal genes When it is Allosomal it s generally known as Pseudoautosomal because it displays autosomal tendencies on a seX gene so it must be present on both 0 MIC Development is present on both SeX Chromosomes SeX Limited o Refers to genes only present on a given Sex Chromosome 0 SRY is only present on the Y Chromosome to induce male development 0 Types I l In uenced Pattern Baldness o Mutation on Chromosome 3 0 Looking at Heterozygotes that s Where the in uence is noted Genotype Female Male Phenotype Phenotype BB Bald Bald Bb Normal Bald bb Normal Normal 0 Why does this happen 0 5d Reductase is present in all people 0 It works on Testosterone to produce Dihvdroxvtestosterone I This acts on the hair follicles o A case study looking at an adrenal gland tumor in a woman displayed an upregulation of Testosterone in her system resulting in all parts increasing I 2 Limited Breast Development 0 Limited is an Either Or sort of thing 0 This only occurs in Females I 3 Sexual Dimorphism Hen Rooster Color 0 This is an offshoot of limited genes that specifically separates phenotypes into male or female 0 Roosters are most colorful and elaborate o Ovary hormones repress color expression 0 Lethal Alleles 12 0 Definition very important alleles critical to proper functioning and survival 0 Genotypic Expressions I With a Homozygous Lethal allele the organism dies so the ratio becomes 12 0 Examples I Manx Cat 0 They lack a tail which has to do with a skeletal spine formation gene 0 But if they have the Homozygous Dominant Genotype because having it all produces defects it is dominant it dies before birth 0 The two mutant alleles messes up spinal development too much I Mice Coat 0 Yellow or Non Yellow coat 0 Scenarios o Homozygous Recessive normal 0 Heterozygous pleiopatry causes negative growth effects 0 Homozygous Dominant death
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