PRINC OF GENETICS
PRINC OF GENETICS BIOL 2153
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Date Created: 10/13/15
Chapter One The Molecular Basis of Heredity Variation and Evolution 11 Modern Genetics has entered its Second Centu Humans have been aware of genetics via selectivebreeding for over 10000 years 0 Cloning can be thought oftaking the most advantageous individuals to 0 do selective breeding in orderto achieve the best resu ts Exploration and understanding ofthe principles ofheredity is a more recent develop men The most important technique in molecular genetics is PCR It starts with a small amount of DNA you put it into a tube t h other reactants and that tube ends up giving you a tremendous amount of O The First Century ofModern Genet39 1 Gregor Mendel published an explanation ofhereditarytransmission in plants in 1866 o H is work was independently rediscovered in 1900 by three botanists o Correns 0 De Vries 0 Von Tsche rmak This was the beginning of modern genetics Extending Mendel39s Analysis Garrod 1901 described the inheritance ofa disorder called alkaptonuria in humans 0 alkaptonuria is autosomal recessive disease that is dueto an eanyme defect that participated in the degradation oftyrosine As a result urine turns a black color within hours Bateso n a proponent of quotMendelis mquot recognized that the trait must be a quotrare recessive character 0 Soon after Sutton and Boveri independently observed chromosome movement during cell division Genes and Chromosomes 0 Genes are the physical units of heredity as originally postulated by Mendel now known to be defined DNA sequences Chromosomes are long molecules of doublestranded DNA and protein which contain genes compacting DNA is crucial 0 Only present for a short period of time in the cell Sexually reproducing organisms usually have homologous pairs or homologs two of each chromosome 0 Humans have diploid number of 46 haploid of 23 o Diploid skin haploid gametes 039 X 39 9lt DOUBLEHELIX 39 4 HISTONES NUCLEOSOME l k m l 4 CHROMATIN Q TIGHTER 3 a lt CHROMSOME Ms nrsuu em mm mm Ms 522M Me an mm A mom Cuncrmosumi mm s som swanun mmuscxvmpzmmem Pairs 122 are the autosomes agelewaj JO aew samosommqa xas aq am 93g Jled Lu 2 Human karyotype Individual is male because on chromosomes SRY gene sex determining regions on chromosome Turner39s Syndrome female onlyhas one X chromosome X0 viable but not fertile Down39s Syndrome Extra letchromosome Kleinfelter39s Syndrome XYY Chromosome Replication The single bacterial chromosome found in the nucleoid region replicates in conjunction with cell division Bacterial Plasmi d chromosome BACTERIA EU KARYOTE In eukaryotes multiple pairs ofhomologs occupy the nucleus 0 Complete sets ofchromosomes are transmitted to identical daughter cells via mitosis um VePllcauun m mama all uiz usis Sexual Reproduction Reproductive cells or gametes are produced by the cell division process called meiosis reduced geneticinfo by 12 males end up with 4 only 1 in females are ovate other three are polar cells Gametes sperm and eggs in animals and pollen and eggs in plants 0 As a result of gametes genes are transmitted to offspring in predictable patterns Early Genetic Concepts Phenotype the observable traits ofan organism Genotype the genetic constitution ofan organism o Genotype Phenotype Phenoxype Blue Eyes Phenotypezamm Eyes Genotype an m as Duminanl is Allelesalternative variant forms ofa gene 0 The study of gene transmission was a foundation of genetics DNA is the heredita material n n mn m n v W34 31 m 3 wi 5wa n 5 During the 19505 the structure and replication of DNA were elucidated Progress in Understanding DNA Function In the 1960s the mechanisms of transcription and translation were laid out This is what is referred to as the central dogma The genetic code was deciphered in the 1960s also By the 19705 cloning and the development of recombinant DNA technology progressed rapidly It was in the mid to late 19705 that there was a tremendous push in these two things because scientists understood that there were some benefits that could be reaped from these technologies Taunon Pram Synlhocm DNA gtFlNA protein 0 Wm DNA Synthesis Tm RNA Synlhuh quotuniversalquot codon table Genomes By the 19805 scientists began to study and compare entire genomes Genome the complete set of genetic information carried by a species 2001 scientific groups in collaboration published a first draft of the human genome Is there a direct relationship between genome size or the number of genes and evolutionary complexity Today we know that there isn t a direct correlation between genome SIZE and complexity 22W Plum mm Naira a mum Maui rim We Ln ee rm lam Wm Emu but transcription does not necessarily imply funcu39on Gene cs Cenu39al to Modern Biology 39 rmnaonmo a hvnmholiral candidate fol the last universal cellular ancestor elhreedomainso 39e o u m true nucleus multiple chromosomes 0 Bacteria no true nucleus single chromosomes 0 uuuiusurmasanes39 39 mmmdh llm m zmmblaMhmlnmmuun M WM l Vimme quotminim TITquot 5quot u quotMWWW m m f r t Furl isms mus Mitochondria and chloroplasts a Plan and animal cells contain mitochondria DNA is the Heredity Material 0 Deoxyribonucleic acid DNA is the hereditary material 0 Ribonucleic acid RNA is used by some viruses usually singlestranded 0 DNA has a doublestranded structure a DNA double helix or DNA duplex 0 DNA replication precisely duplicates the DNA duplex prior to cell division 0 In transcription one DNA strand is used to direct RNA synthesis 0 Messenger RNA mRNA undergoes translation to produce proteins at nucleoprotein structures called ribosomes Modern Genetics Has Three Major Branches 0 Transmission genetics Mendelian genetics is the study of the transmission of traits in successive generations single gene traits are much easier to predict and examine o Evolutionary genetics studies the origins of and genetics relationships between organisms and evolution of genes and genomes 0 Molecular genetics studies inheritance and variations of nucleic acids and proteins Single gene traits in humans 0 Many traits in humans are NOT controlled by one gene but MANY genes 0 Eye color height hair color etc 0 Several traits in humans are controlled by ONE gene making it easy to determine your phenotype and possible your genotype 0 Let s examine a few for fun 1 2 The Structure of DNA Suggests a Mechanism for Replication 0 Identification of DNA as the hereditary material was the foundation ofnew molecularfocused approaches in biological research 0 The molecular structure of DNA was key to understanding 0 How DNA could carry genetic information o How the molecule replicated accurately replicated The DNA Double Helix L w r r o Other researchers made significant contributions to understanding DNA structure Rosalind Franklin o Xrays that pass through the crystalized structure are diffracted creating a u attern collected on Xra film Erwin Char aff v v I A39H H M w QUESTION If an organlsm has 22 cytosme content wha T and G do they have C22 G22 A28 T28 o QUESTION I have a sample of DNA from an organism that is 10 A 20 C 30 G 40T Is that possible Why sonot so Single stranded DNA t percent A DNA Nucleotides 0 DNA nucleotides are composed ofa Deoxyribose 5carbon sugar a phosphate group and one of the four nitrogenous bases designated 0 Adenine A o Guanine G o Thymine T o C 39 V 391 o Peptide bonds between amino acids that are very strong Complementary Base Pairing o Complementary base pairing occurs between an A on one strand and a T on the other or a G on strand and a C on the other 0 Hydrogen bonds form between the complementary base pairs across the two strands A hydrogen bond is relatively weak In a large group this is what keeps the molecule held together Hydrogen bonds are able to be broken eamplmunmvy I has pain 5 ComplemnIry lugwholp39lIm nunquot 5 Juanaquot I quotr Wri 1 quot t Wquot Phosp o I 3 I I WWW r mun Sound 2 539 phosphate Nuullolidl blu arwv 7 a amm Wash Thydvoxyl I 5m 51 Dcoxylibosu pnoapnwienu ygm 3329 bond y A 4 quotn I Yhymine Adanlnn DNA Replication 0 Each single strand of DNA contains the information needed to generate its complementar strand o Semiconservative replication creates two new duplexes each composed of one parental original strand and one newly made daughter strand 1 3 Transcription and Translation Ex ress Genes U iquot quotu H1 a Replication Transcription Translation DNA gt1 J gt Protein Types of RNA 0 Several types ofDNA are produced in a cell messenger RNA mRNA is the only type that is translated o Ribosomal RNA rRNA forms part of the ribosomes it feeds the mRNA between the two subunits kind oflike threading a needle during translation it brings in individual amino acids onto the tRNAs 0 Transfer RNA tRNA carries amino acids to ribosomes to be assembled into proteins Additional Features of an Updated Central Dogma 0 Reverse transcription uses transcriptase and an RNA template from RNA containing viruses to produce complementary DNA 0 MicroRNAs are small RNA molecules with roles in regulation of gene expression in plants and animals Repllnatinn Transcrlpllon Transallay DNA Messenger u mRNA Protein K Ribosomal mun ransier 1mm me mm Micro miR mm 77777777 if numvirus Reverse lransmptian Transcription Transcription uses one strand of DNA to direct synthesis ofa singlestranded RNA transcript The DNA strand from which the RNA is synthesized is called template strand 0 The complementarypartner ofthe template strand is calledthe coding strand vs the noncoding strand Coding DNA 539 ATGGTGCACCTGACTCCTGAGGAG 339 strand 3 TACCACGTGGACTGAGGACTCCTC S39Template strand The DNA coding strand and the mRNA transcript havet e same polarity and sequence substituting U in mFtNA forT in DNA Features of RNA 0 RNA consists of ribose a phosphate group and one of four nucleotide bases three ofthese A C and G are the same as DN U racil replaces thymine in RNA U pairs with A in RNA RNA complementary base pairin NA polymerase is the enzyme that synthesizes RNA transcripts Regulation of Transcription Promoters help regulate the initiation oftranscription which begins near the promoter site at the start oftranscription they are typically very close to the start ofthe transcription site Transcription ends at the termination sequence Eukaryotic genes have exons with coding information and introns that are removed from the transcript prior to translation DNA 5 1 Emma can sequonc 0 L 2 h E 1 E 2 E a DNA 539 gramme 339 5 39 Translation 0 Translation converts the genetic message carried by mRNA into a sequence of amino acids joined together by covalent peptide bonds at the ribosome The resulting polypeptide upon folding makes up all or part ofa protein Each amino acid is specified by a codon three consecutive nucleotides on the mRNA The Beginning of Translation 0 Translation begins when mRNA attaches to the ribosome in a manner that places the start codon in the correct position 0 The start codon is usually AUG from here ribosomes move in the 5 to 3 direction along the mRNA to assemble the specified amino acid chain a bl Amlnn acid nlypep do P 39 Pepuuenond 7mm a 39 All d LL J39ncuan DNA Coding strand Ejmm Template strand 3 J 5 DNAtripiet1 2 3 4 5 6 7 mRNAS39JES Q Codonz1 2 3 4 5 s 7 manyi ga g Polypeptide 539 39 2 mm Aminoacidsequence1 2 3 4 5 SSTOP V 1 3 5 Vi Slapcudnn 7 The Process of Translation 0 Amino acids are transported to ribosomes by tRNAs o Complementary base pairing takes place between the mRNA codon and the anticodon of the tRNA and allows for the correct amino acids to be added to the chain 0 When a ribosome reaches one of three stop codons UAA UAG or UGA translation ceases this is a signal or a cue that the substances should disassociate from each other The Genetic Code 0 mRNA specifies an amino acid sequence using the genetic code 0 There are 64 possible triplet codons read in the 5 to 3 direction each specifies one amino acid There are 20 common amino acids 0 Some amino acids are specified by one codon and others by up to six different codons 1 4 Evolution has a Molecular Basis 0 Life is not static or uniform it evolves as DNA acquires mutational changes hanes are counted at the level of the DNA se uence 7 ID i a 0 Life of Earth most likely originated from a single source 3540 billion years ago the earliest known fossils appear similar to bacteria that exist today Darwin39s Theory of Evolution 0 Since life originated millions of species have come and gone these changes occurred throu h evolution 1 llC i1ampaielu tum w leirl 0 As one morphological form is favored over another the frequencies of alleles associated with each form are altered o Darwin s theory is now firmly established Darwin s Principles of Populations 0 Variation exists among members ofpopulations regarding the expression of traits 0 Variation of traits is passed from one generation to the next 0 Certain variant forms of traits give individuals that possess them a higher rate of survival and reproduction these traits are passed to the next generation with higher frequency Darwin s Principles of Populations are supported by Biological Findings 0 Phenotypic variation re ects genetic variation allele variation 0 Offspring inherit and express the alleles responsible for phenotypic variation in their parents 0 Organisms carrying certain allele variants have a reproductive advantage over those who do not Four Evolutionary Processes o Evolutionary genetics examines genetic changes in populations and species over time o Evolutionary hypotheses have been tested and verified countless times in nature and laboratory settings 0 Evolutionary biology has confirmed Darwin s model and expanded the description of evolutionary processes Modern Synthesis of Evolution The modern synthesis of evolution merges evolutionary theory with experimental and molecular population biology It provides a unifying View of evolution It gives a clear and nearly complete picture of the factors and mechanisms that produce evolutionary changes in populations Tracing Evolutionary Relationships Evolutionary relationships among organisms can be depicted in a diagram called a phylogenetic tree The most commonly used approach is the cIadisticapproach which sorts evolutionary relationships into groups called cIades Members of a clade have shared derived Characteristics either morphological or molecular Ground llnches eed caters Large Medium Small 9 Large 7 cactus 3 ch15 2 3 eaters Tree nches Imet eaters Mangrove f Vegelarian r Bud nch 3quot eater Sharphealed Seed nch 3 ea 7 WIIBIBI nches Insect ca er Common Gm ancestor Green 1 Working with a Phylogenetic Tree I Knowing the evolutionary relan39onship of a group of organismsimproves understanding oftheir biology The tree nches Fig 113 form a monophyleticgroup which includes a common ancestor and all ofits descendants Insecteating finches Fig 113 form a paraphyleticgroup one that includes a common ancestor but only some ofthe descendants Polyphyletic lacks a common ancestor MONO PARAPHYLETIC Z A polyphyletic group lacks common ancestor Paraphylen39c groups made up of ancestor and some but not all of that ancestors descendent species Example I is missing monophyletic made up of ancestor and all descendant species All share a single common ancestor Constructing Phylogenetic Trees Using Morphology and Anatomy 0 To construct a phylogenetic tree consider the common morphological features shared by groups of the organisms under construction 0 Find an outgroup an organism lacking a feature shared by all ofthe others in the ingroup O nce co mplete the tree can be used to infer characteristics of ancestral spec1es Mmphalngle channellsucs mum vmmm ladn cmmduu 5mm Constructing Phylogenetic Trees Using Molecules Phylogenetic trees based on molecular features are constructed based on shared features that are in DNA or protein sequences 0 Shared characteristics that evolved independently arise by convergent evolution or homoplasy bird vs bat wing Shared features used to construct phylogenetic trees must not have evolved independently Terminology we need to define Analogous performs the same mction but are structurally di ferent 0 Human legs vs insect legs Both used for movement but structure are different o Wimilarsnucture anammicalbabutperforms di ferentfunctions 0 Human arms vs front whale ipper Bothlook as though are arm structures 0 Humans hold items while whales use fins to swim Evolution Processes Convergent Evolution different taXaspecies solve a problem in the same way evolutionarily This examines analogous charac ers 0 Ex front ippers ofwhale and front fins offish both used to swim but one is mammal and one is fish Divergent Evolution process by which an ancestral characteristic becomes adapted to new roles This examines homologous characters 0 EX human arms and wings ofbats There is a common ancestor to both organisms which had 4 limbs In humans the one pair evolved into armshands used for holdinggrasping and in bats they evolved into wings for ight Chapter Two Transmission Genetics 21 Gregor Mendel 18221884 Discovered the Basic Principles of Genetic Transmission Mendel obtained 34 different varieties ofpeas and examined the characteristics of each He identified 14 strains representing 7 specific traits each with two forms that could be easily distinguished He worked with these strains for 5 years determining how each character was inherited l 1911 i Seed P d Flo er Plant 1 color 2 shape 3 color 4 shape 5 color 6 posilion 7 height interior mature mature E m quota 9 l E r a 4m E W N g s o a 0 0 yellow round green inflated purple axial lall 7284quot a w 539 V g l 395 5 6 0 M green wrinkled yellow white terminal short 1824quot Mendel s Work was not a u reciated at First The scientists of the day did not understand the significance of Mendel s experiments In 1900 his work was quotrediscoveredquot and a revolution in biology was launched Mendel s experimental approach was in part in uenced by his training in physics His success stemmed from his counting the individuals with each trait in his experiments He chose the pea an organism that was easy to work with and had many available varieties they are very fertile and hearty and easy for a skilled botanist like Mendel to manipulate and cross breed The Blending Theory of Inheritance Mendel s experiments tested the blending theory ofheredity It Viewed the traits in offspring as a mixture of the parental traits Under this theory a black cat and a white one if crossed would produce gray kittens and that the original black and white colors would never reappear if the grey kittens were bred with one another Mendel39s Approach Followed the Modern Scienti cMethod Make initial observations about a phenomenon Formulate a testablehypothesis Design a controlled experiment to test the hypothesis Collect data from the experiment Interpret the experimental results comparing them to those expected under the hypothesis Draw a conclusion and reformulate the hypothesis if necessary One of Mendel39s strengths was his careful experimental design WPWN 0 Five Critical Experimental Innovations There were five features of Mendel39s breeding experiments that we re critical to his success Controlled crosses between plants Use ofpurebreeding strains to begin experimental crosses Selection ofsingle traits with dichotomous phenotypes Quantification of results Use of replicate recip rocal and testcross analysis WPWN 1 Controlled Crosses between Plants Pea plants are capable ofselffertilization and artificial crossfertilization Selffertilization occurs naturall Crossfertilization involves removing the anthers from a flower and introducingpollen ofthe desired type with a small brus By preventing naturally occurring crosspollination completed by insects he could manually control fertilization events FenilizaIinn Emucuhh wry llmu Ymnslevpnllcu mm mm quotuer by removing mm M quotmm a In purple mm mm m mum mm pom x v u Q Plant mamminn ower development mum Seed development mm 959 V Fernllxlem anew Q w39 l 7 l 39 39 l sum dwYID Mature seeds 2 PureBreeding Strains to Begin Experimental Crosses o Mendel took 2 years prior to beginning his experiments to establish pure breeding or truebreeding strains These are strains that consistently produce the same phenotype as itself Each experiment began with crosses between two purebreeding parental generation plants P generation that produced offspring called F1first filial generation 0 Further Experiment Crosses 0 F1 offspring that are crossed to one another produce the next generation of offspring the second filial generation F2 0 These can be crossed to produce the third filial generation F3 and so on as needed Purebreeding Purebreedan purple flower while flower F x F Purple flower progeny plants I SelMerlilized F or arlilicially terlllized F Eurple furpie Purple White uh Selilerlilized F2 or artificially fertilized F F FJ generallon 3 Selection of Single Traits with Dichotomous Phenotypes Each of the traits Mendel chose had just two possible phenotypes or dichotomous forms 0 These were easily distinguished from one another with no intermediate phenotypes 0 Early in his experiments he worked with an additional trait but discontinued it when he noticed a connection with another trait 4 Quantification of Results 0 Mendel counted the number of progeny plants of each type and counted many offspring from each cross 0 He identified patterns in his results such as the consistent ratios between 5 Replicate Reciprocal and TestCross Analysis 0 Mendel made many a Reciprocal crosses Purebreeding Purebreeding Pure breeding Purebreeding pollen egg pollen egg 9 9quot 99 95 GO P x x on Artificial crossfertilization Ani clal crossfertilization F F Gg 6 Reciprocal crosses between purebreeding parents produce identical results Cross A O x ed to Offspring all yellow b Test cross Genotype unknown 0 Purebreeding X rr Artificial cgssfer lilizaiion A 11 ratio of dominant to recessive is expected if the round seed is heterozygous Rr all progeny are dominant if the round seed is homozygous Rn Crass B Mendel s carefully planned and executed experiments and precise analysis disproved the blending theory of heredity and produced a new theory All of the traits Mendel studied gave consistent results Purebreeding parental strains were artificially crossfertilized to produce an F1 generation these were selfcrossed or intercrossed to produce F2 All of the F1 produced had the same phenotype eg when yellowpea and greenpea parents were crossed all the F1 had yellow peas Dominant and Recessive Traits o The trait shown by the F1 offspring was called the dominant phenotype yellow peas eg o The trait that was not apparent in the F1 was called the recessive Homozygous parent Gnmexe tormution contributes only one a allele of the gene 9 Fortll lzatlon F hoterozygotes display F the dominanl phenotype I seen in one parenl Gamoto lormallon and sell nrtlllzotlon F Segregallon ol alleles from heterozygous cg prouucos a l n g conlalnlng gamales at equal l requanlzy Punnott square Gonolyple ratio Phenotypil ratio Random union ol gametes H ou ac to form the F2prodlces a Heterozygous a an 3 yellow 1 21 genowelc rag0 and 3 Heterozygous A a 31 Phenotych rato omozygous 3 as 3 1 green Consistent Results of These Experiments 1 Dominance of one phenotype over the other in the F1 generation 2 Reemergence of the recessive phenotype in the F2 generations 3 A ratio of approximately 31 dominant recessive among F2 phenotypes Evidence of Particulate Inheritance and Rejection of the Blending Theory 0 Mendel s results rejected the blending theory of heredity o Mendel proposed the theory of particulate inheritance o The theory states that plants carry two discrete hereditary units for each trait a plant receives one of these in the egg and the second in the pollen Alleles o The hereditary particles referred to in theory are alleles alternate form of an allele 0 Together the two alleles for each trait determine the phenotype of the individual 0 Mendel used letters as symbols to represent the alleles for each trait Homozygous and Heterozygous Individuals 0 Purebreeding individuals like Mendel s parent plants have identical copies of the two alleles for a trait referred to as true breeding 0 These are called homozygous individuals AA aa same alleles o The F1 plants had different alleles from each parent and were heterozygous Consistent Inheritance Patterns among All Traits Studied b Mendel o The F1 plants are crossed or allo 39 39 n m quot1 m 1 Hi L p y n m mid by 39 39 gm m w r gCHOWPiC phenotypic ratio ration doesn t always equal Segregation of Alleles o The Punnett Square method of diagramming a genetic cross is a simple tool of genetic analysis 0 The alleles in gametes carried by one parent are arranged along the top of the square and those of the other parent down the side 0 The results expected from random fusion of the gametes are placed within Pure Pure an rr P 9 O Cross Ierllllzaxlan H 99 5 Pgrquot TEE cross a domlnant F quot plan to a recessive plum F 0 x 0 lo delarrnlna n the F is I I heierozyguus Tealcross cannnnzauon F a r g J39 a u r 9 o I ma F Is heterozygous quot r n this ratio at gnmalea g wllba11l unn aqua In Mendel s testc7053 experiment he Iounc 193 mum nna 192 wrlnklod Kast zroaa pmgeny a 1911 ran Mendel39s First Law J quot o The law applies to all seven traits tested Hypothesis Testing by TestCross Analysis 0 Based on his segregation hypothesis Mendel expected that half of the gametes of heterozygous F1 individuals would carry the dominant allele and half the recessive He tested this by crossing suspected heterozygous individuals with homozygous recessive individuals from a purebreeding stock He predicted that 50 of the offspring of this test cross should have the dominant trait and 50 the recessive Hypothesis Testing by F2 SelfFertilization Mendel39s hypothesis predicts that F2 plants with the dominant phenotype can be homozygous orheterozygous The heterozygous state 23 is twice as likely as the homozygous state 13 0 He used a selffertilization experiment to test the predictions ofthe hypothesis Results of SelfFertilization Experiments Agreed with Predictions Mendel expected that homozygous F2 plants should produce progeny with the dominant phenotype only 0 He expected that heterozygous F2 plants would generate a 31 ratio of dominant recessive phenotype amongtheir progeny These predictions were confirmed by the experimental results 23DihybridCross Analysis of Two Genes To study the simultaneous transmission oftwo traits Mendel made dihybrid crosses between organisms that differed fortwo traits He began each cross with purebreeding lines eg RRGG and rrgg and produced F1that were heterozygous forboth traits eg RrGg Ifassortment is random four gametes shouldbe equallylike in the F1 eg RG Rg FG Fgl Pure round Pure wrinkled yellow green RIG nag P 0 x 3 Gamete formation R6 399 Crossfertilization 8165 no An Aid to Prediction of Gamete Frequency 0 The forkedline diagram is used to determine gamete genotypes and frequencies Genotype Frequency Heterozygous ln quot 39 39RG l quot 69 Gaaepggmng VVVVVVV aghi o QITBFGW a 1 r 2 lguurg WM Prediction of the Results of Genetic Crosses o A Punnett square is used to illustrate the random union of all types of gametes produced by the parents in a cross 0 In the case of the Dihybrid crosses performed by Mendel the Punnett Square illustrates the phenotypic ratio he observed in the F2 0 The Dihybrid ratio 916 both dominant traits 316 each for two combinations of one dominant and one recessive and 116 both recessives Summary HG in 1 Hi i r9 Genotypes Phenotypes nl inn 39 39 1 M Jalrog Rec m 1H IIGG O O O 0 may 0 erg 1439 39 quotquot 1quot quotquot n will gy r i gg l gg 15 0 0 0 9 9 in when 16 lr g 95mm 93169 quotIn i quotG quot69 6 1s 0 9 C C O in lr g lrgg array 11 rrgg ngg f 1 15 rrgg 0 9 O U 0 Mendel s Second Law m l e l H l Heterozygous Heterozygous Brag r g F x Gamele formation no lg 16 19 l Sellfertilization F generation Round yellow ll G 315 parental Houndgreen n gu 108 nonparental Wrinkled yellow quot6 101 nonparental Wrinkled green vrgg 32 parental Fz phenotype ratio by trail a round 315 108 423 wrlnkied 101 32 13 Mendel39s dihybridcross 423 133 318 1 experiment produced a D VEIIOW 315 101 415 and a 9331 ratio lor the green 108 32 140 combined phenotypes 416140 237 1 F2 phenotype ratio by trait 315 108 101 32 934 338 318 1 Independent Assortment ofAlleles from the RrGg x RrGgCross Mendel predicted that alleles ofeach locus unite at random to produce the F2 generating Round yellow RG 34 34 916 Round green R gg 3414 316 Wrinkled yellow rrG 34 14 316 Wrinkled green rrgg 14 14 116 Testing Independent Assortment by TestCross Analysis 0 To test his hypothesis about independent assortment Mendel performed testcross analysis He predicted that the F1 seeds we re Dihyb rid of genotype RrGg and that crossing them to a plant of genotype rrgg would yield four offspring phenotypes with equal frequency 52 5quot p g x c 4 i 1 v m a mm m m rrgg as x o i WWW 1 mm 07 mm 7 r gleam 9355va p25 55 also Ms 51 must n25 as may mg 3mm ma mnmnn Tn mm pmgnny am absawud in display but Fhennly u in nunI lv unncias n5 Denied by IPPIicl an a Mendel i aws Testing Independent Assortment by Trihybrid Cross Analysis 0 To testhis hypothesis about independent assortment further Mendel performed the trihybridcross analysis The trihybridc ross involved three traits round vs wrinkled peas yellow vs green peas and purple vs white owers The cross was RRGGPP X rrggpp the F1 were RrGgPp Mendel Compared Predicted Outcomes to Actual Results of the Trihybrid Crosses o The number of gamete genotypes can be expressed as 2quot where n number of genes 0 In a trihybrid cross eight different gametes are possible each equally likely 18 0 Using the 1 expected frequencies for each individual trait a phenotypic ratio expected for F2 progeny can be generated Probability Calculations in Genetics Problem Solving o A Punnett square can be used to determine the phenotypes expected in a cross such as a Dihybrid cross The independence of the genes in the cross gives a quicker way to predict this by multiplying the probability of the phenotype at one locus 34 or 14 by the probability of the phenotype at the second locus also 3A or Mi This can be applied to any number of genes in a cross 24 Probability Theory The Product Rule AND m m 39 w m WWM o This is the product rule also called the multiplication rule Probability Theory The Sum Rule OR o The sum rule is also called the addition rule w v u 39 U 39 mquot on UNquot 13h mm Lialmcwrm m Probability Theory The Conditional Probability o The product and sum rules are used before a cross is made in order to predict the likelihood of certain outcomes Conditional probability involves questions asked after a cross has been made and is applied when information about the outcome modifies the probability calculation Example 1 of Conditional Probability P1 RRYYTTSS X rryyttss F1 RrYyTtSs X RrYyTtSs What is the probability of obtaining the genotype RrYyTtss Y Y Tt Tt RrXRr 1X 1 X Ss 1RR2Rr1rr 1 YY 2 Yy 1 yy 1TT 2Tt 1 tt 1SZSs1ss 24 Rr 24 2 4Tt 4 ss 0 Probability of obtaining individual with Rrand Yyand Ttand ss 24x24 x24x 14 8256 or 132 Example 2 of Conditional Probability p Run39 ssunym mvms my ns F What i m pmbumnw ul39vl mnmlg a mum Gcnnmvc wuhl m mm39r Iy harmguus gcnmw39 mm Rum Tun Ssxslt lRKIerrr incwm mznm mmm HRH HV39Y mTr 1453 4quot K Nu m lllxlxlehwl xlLdxlill Probability Theory Binomial Probability Some questions involve predicting the likelihood ofa series of events for which there are two outcomes each time 0 We usebinomial probability calculations to answer this type of question 0 It expands the binomial eXpression to re ect the number ofoutcome combinations and the probability ofeach Construction ofa Binomial Expansion Formula Abinomial expansion contains two variables p the frequency ofone outcome and q the frequency ofthe alternative outcome p and q may or may not be equal depending on the type of outcome 0 p q 1 since these are the only two outcomes 0 We eXpand the equation by the power of n where nnumber ofsuccessive events p qn Binomial Expansion Formula Example For families with three children predict the proportions with each possible combination ofboys and gir s P probability ofa boy 12 11 probability of a girl 1A Binomial eXpansion pq 3 p33p2q 3qu 3 P3 18 3 boys 3p2q 38 2 boys 1 girl 393qu 38 1 boy 2 girls 113 18 3 girls Application of Binomial Expansion to Progeny Phenotypes In a selffertilized Gg pea plant give the proportion ofyellow and green peas in pods with sixpeas each P probability of yellow peas 3A1 Q probability of green peas 11 A shortcut to the binomial expression is Pascal39s triangle which is easy to calculate Total number of combinallons l7 1 1 1 1 1 z 2 1 2 1 4 Z 1 3 3 1 8 4 1 4 4 I 16 5 1 5 1D 10 1 32 5 1 S 15 20 15 6 1 54 7 l 7 21 35 35 21 7 1 1 28 5 I 23 56 7D 25 E 1 256 9 1 Q E 84 125 1 2 4 35 9 1 51 2 1a 1 ID 5 120 2 0 252 210 20 45 10 1 1024 11 1 11 55 1 55 330 462 4352 330 155 55 1 1 1 2045 12 1 12 65 220 495 792 924 792 495 220 55 12 1 4095 u at W J 11 mm 511mm 5 mm 5 19111111 a 111m 1 191111 2 yellow 1 yellow 0 yellow 111115111 115 1111111 11111 2115 1 111 1119 511 s 11131 Mum u1 12331 1 a 15 11 15 1 50 11191quot mmuw 1 a must 0 P Sp q 1 S l ZOP q 1 EFxG 594 q 1 Im 111mm 1 g cm mg 111 111 H356 11291 11132 1111 1111111 11111111 1m i i 25 ChiSquare Analysis Tests the Fit Between Observed and Expected Outcomes Scientists must be able to objectively determine whether results are consistent with expectations The chisquare test X2 was developed to allow for these objective comparisons In large samples outcomes predicted by chance have a normal Gaussian distribution This is often described as a quotbell shaped curve The mean u is the average outcome and other outcomes are distributed around the mean The probability ofan experimental outcome gets smaller the further it is from the mean The Probability ofParticular Outcomes Probability ofparticular outcomes is quantified by a measurement calledstandard deviation 6 In a normal distribution 682 of all outcomes fall within one o ofthe mean 954 within 26 etc experimental outcome that is more than 26 from the mean shows a statistically signi cant difference between the observed and expected outcome m 3 S a An Idsallzed a g normal dislribuh un E a z a a 4quot A2 p 2quot 3quot l l 682 551 995 The ChiSquare Analysis The chisquare x2 test is commonly used for quantifying how closely an experimental observation matches the expected outcome 0 Z O iEjzE 0 observed Values E expected Values 0 The interpretation ofthe test is done by a means ofa probability P value 0 It is the probability that the results ofanother experiment ofthe same size and structure with deviate as much or more from the expected results by chance Low xi values are associated with high Pvalues chance alone likely explains the deviations The Pvalue for an experiment is dependent on the degrees offreedom DFequal to of classes being observed minus 1 0 Framing a Hypothesis Null Hypothesis observed values are not different fromthe expected values 0 39 observed values are different from expected values Statistical Significance A statistically significant result from xzanalysis is one for which the P value is less than 005 0 When any experimental result has less than 5 probability the hypothesis of chance is rejected 0 P values above 5 indicate a significant deviation between observed and expected values 0 This results infailure to rejectthe hypothesis of chance So what does rejecting the Null Hypothesis versus NOT rejecting the null hypothesis Deviations NOT due to chance alone ChiSquare Analysis of Mendel s Data Modern statistical methods allow us to test Mendel s experimental data for compatibility with his laws From statistical analysis of his data we can conclude that the results are consistent with the predictions Be careful not to quoteyeballquot values Differences must be verified statistically x2 Example Monohybrid Cross For round vs wrinkled seeds Mendel OBSERVED 5475 round and 1850 wrinkled from his monohybrid cross Rrx Rr for a total of 73 24 seeds The EXP values 7324 34 5493 round R and 7324 14 1831 wrinkled rr x2 OBS EXP2 EXP 0263 For DF 1 the P value falls between 050 and 090 well above the 005 cutoff value Deviations just due to chance alone X2ltCV therefore deviations just due to chance alone 76 lt CV Therefore deviations just due to chance alone TABLE moannu pVa t ow 539wa a I m 1 0 ans 0 5 UW 3m I l 1 an a In ml AM Hm H 2 j on am l w u we 7 ma i 7 1 7 7 i i 3 j in M l 21 us gr n n if l X2 i mo ms j m n 4 H2 54 3 GI A7quot 05 Deviations just due 0 chance alone Deviations NOT due to chance alone Trihybrid Cross quotm quot 39 39 quotquotquot 39quot mm wnmnm Mendel39s Observationquot Number Expetred These are the EXP calculations then7va um 34 mund yellow purple 2764 or 0422 9 Roundyelluwmumle 25 lease 3 round e yellow while 964 or 0 141 gt Round yLllow wmre ya seas round green purple 964 or 0 141 Igt Round green W39P E Eb 5985 A round green39A while 364 or 0047 ET launaemmwm 2 was we wrinkled yellow purple 964 or 014 gt lvnnurayelvwmmwe as am A wrinkledx A yellow 4 whte 364 or o 047 gt wmumvelmwmw u was A wnnkledll39A green purple 364 or 0047 gt nun12mm rum2 in ms 2 wrnkledl 4 greenWA while 164 or 0016 gt Wlnkledralmrwlllv 519 53399 17269 lye e marma mus 1 I r m 7 25955 lsa Au l39 X1 lt CV e lEB e wearam Theremre 7 up 7 waslaws A l7 7 synfeat 7 m devlatlons m 7 Just due 10 mm a 090 chance 1X1 alone Central Conclusions from Molecular Studies of Mendel39s Traits 1 Inheritance of alleles precisely parallels the pattern oftransmission of morphological variants Morphologic variation results from differences in structure and function of protein products ofthe a e es Molecular analysis led to identification ofDNA sequence differences between alleles and their consequences Functional analysis ofthe protein products ofeach allele led to understanding of its function in producing the phenotype 5x 5 P 26 Autosomal Inheritance and Molecular Genetics Parallel the Predictions of Mendel39s Hereditary Predictions o In the early 19005 biologists began to extend Mendel39s findings to other organisms 0 They also began to identify exceptions to the hereditary principles 0 Mendelian principles can be applied to transmission of certain traits in umans Autosomal Inheritance o Autosomal Inheritance refers to transmission of traits carried on autosomes chromosomes found in both males and females 0 There are two copies of each autosome so each individual carries two copies of each autosomal gene 0 Individuals with two identical copies are homozygous those with two different copies are heterozygous o X linked inheritance addressed later in semester Pedigrees Pedigrees or family trees are a way oftracing the inheritance oftraits in humans and some animals A standard notation is used to indicate males and females their relationships and the individuals who show the trait and those who do not The generations are indicated by Roman numerals symu Female Male 0 Do no mm m 0 ID Exwess lml o Hexumlygcus carriers or a rewiilve allele Deoeam a noun am a dealquot Llnes l EU unspecllleu sex Genam on 7 Parenls warm closnlv milled by blood Aduptinn l ll l Slmlngs mm mm rmemal wills Numbers ML Ill 4 Ram n3 em Arahl quotmum duals In a geneullon Autosomal Dominant Inheritance There are 6 characteristics ofthis mode of inheritance 1 2 3 4 Each individual who has the diseasehas at least one affected parent Males and females are affected in equal numbers Either seX can transmit the disease allele In crosses where one parent is affected and the other is not approximately half the offspring express the disease u affected parents will not have any children that express the disease Two affected parents may produce unaffected children l mo l lili 9 ll m 39vID ITS THCl all l I quot I 7 13 in Ll Disease E acl lncldenca o Diseasa Hyparcholeskemlemla Mlsslng protein that removes 1122 French chromosome 19 cholostnrol from the blood heart Canadians attack by age 50 HunUngton dlsezse Pragrasslve manlal and 11253100 Caucasians chromosoma 4 neurologlcal damage neuraloglc disorders by ages do 7o Autosomal Ther Recessive Inheritance e are 6 characteristics ofthis mode of inheritance 1 Individuals who have the disease are often born to parents who do N Sn 9 not have the disease If only one parent has the disorder the risk that a child will have it depends on the genotype ofthe other parent lfboth parents have the disorder all children will have it The sex ratio of affected offspring is expected to be equal The disease is not usually seen in each generation but if an affected child is produced by unaffected parents the risk to subsequent children is 1A Ifthe disease is rare inthe population unaffected parents of affected children are likely to be related to one another 160r11
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