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Mendelian Genetics

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Slide 1Genetics: The BasicsSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Dihybrid CrossSlide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Sex Linked TraitsSlide 46Slide 47Slide 48Y Linked TraitsSlide 50Slide 51Slide 52Slide 53Slide 54Common Heritable TraitsSlide 56Slide 57Slide 58Slide 59Case Study: In Sickness and In Health Greg and Olga’s Trip to the Genetic CounselorPart 1: Pedigree Construction 10 minutesSlide 62Part 2: Autosomal Dominant Traits 10 minutesPart 3: Autosomal RecessiveTraits 10 minutesSlide 65Part 4: Sex-Linked Inheritance 10 minutesMendelian GeneticsGenetics: The Basics•Allele- An alternative form of a gene•Diploid organisms have one copy on each homologous chromosome–Represented by letters:•Capital letter = dominant form •Lower case letter = recessive form•Example= Eye Color–Controlled by 2 alleles –Blue Eyes = bb–Brown eyes= Bb or BBDominant allele-fully expressed in the organism's appearanceRecessive allele-no noticeable effect on the organism's appearanceGenetics: The Basics–Heterozygous: Have 2 different forms of the allele•Example:–Brown Eyes = Bb = heterozygous–Homozygous: Have 2 of the same forms of the allele•Example: –Blue Eyes = bb = homozygous recessive–Brown Eyes = BB = homozygous dominantGenetics: The Basics–Genotype = the genetic makeup of an organism•Example = BB, Bb, bb–Phenotype = the physical expression of genes•Example =–Brown Eyes = phenotype of either the BB or Bb genotype–Blue Eyes= phenotype of the bb genotypeRemember that phenotype is not necessarily an appearance-It can be things like enzyme production, behavior, etc!!It is ANY expression of a gene!!Gregor Mendel*1843 entered monastery*1851-53 studied at Univ. of Vienna*1857 started breeding garden peas* 1860 started forging data!!MENDEL'S MAIN QUESTIONDo units of inheritance retain integrity (preserved) or blend????Sample Question: If you cross a purple flower with a white flower are these flower colors retained in future crosses or are they blended to form an intermediate color?Law of Segregation-two alleles for a character are packaged into separate gametes2 plants crossedSelf-fertilizedMendel's findings1. Alternative version of genes (alleles) account for variations in inherited charactersPurple flowersWhite flowersHomologous chromosomesMendel's findings2. For each character, an organism inherits two alleles, one from each parent.Purple flowersWhite flowersmaternalpaternalHomologous chromosomesMendel's findings3. If two alleles differ, the dominant allele is fully expressed in the organism's appearance.Purple flowersWhite flowersrecessivedominantMendel's findings4. The two alleles for each character segregate during gamete production.dominant recessivePP ppSeed shapeP pGametesPunnett SquarePredicts the results of a genetic cross between individuals with known genotypesRules for Genetic Problems1. Identify traits (alleles) and assign letters to represent the various traits: capital letters for dominant traits; lower case letters for recessive traits.3. Draw individual gametes with corresponding letter for trait.2. Set up parental cross.7. Set up Punnett square to identify individual genotypes and phenotypes for F2 offspring.4. Identify F1 offspring phenotype and genotype.5. Setup F1 cross.6. Draw individual gametes with corresponding letter for trait.EXAMPLE: SEED COLORdominant recessiveCC cccCccCCcCCC Cc Cc cc 3 1EXAMPLE: POD SHAPEdominant recessivesSssSSsSSS Ss Ss ss 3 1 SS ssMonohybrid CrossFollows single traitTest CrossBreeding a homozygous recessive with a dominant phenotype (unknown genotype) can determine an unknown allele.In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? SsSsF1 generation, test cross:What is the genotypic ratio?What is the phenotypic ratio?The test cross To identify the genotype of yellow-seeded pea plants as either homozygous dominant (YY) or heterozygous (Yy), you could do a test cross with plants of genotype _______. A. y B. Y C. yyD. YY E. YyPredicting the results of a test cross A test cross is used to determine if the genotype of a plant with the dominant phenotype is homozygous or heterozygous. If the unknown is homozygous, all of the offspring of the test cross have the __________ phenotype. If the unknown is heterozygous, half of the offspring will have the __________ phenotype. A. dominant, recessive B. recessive, dominant•Question: How are two traits inherited? •DIHYBRID CROSS•Experimental Approach: A cross involving two true-breeding traits. System: Pea Plants; seed color (Y/y) and seed shape (S/s).F1 GenerationF1 Generation1. Each of the male gametes types (SY, Sy, sY, sy) can fuse with each of the female gametes types (SY, Sy, sY, sy). 2. 16 possible combinations of gametes are possible. 3. We will see that there are 9 possible genotypes and 4 possible phenotypes. 4. The two parental phenotypes, and two new phenotypes were obtained. F1 GenerationDihybrid CrossFollows two traits9:3:3:1 RATIODihybrid CrossLaw of Independent Assortment-separation of alleles into separate gametesInheritance that diverges from Mendel's inheritanceGENE INTERACTIONSThe relationship between the genotype and phenotype is rarely simple.* Each character is rarely controlled by one gene*Each gene usually has more than two alleles, with not always being dominant over the otherIncomplete DominanceHeterozygotes show a distinct intermediate phenotype, not seen in homozygotes Not BLENDEDTraits are separable in further crossesMost genes have more than two alleles in a population. (IA, IB, I)In CODOMINANCE, both alleles are expressed and functional, though they may be different.PleiotrophicMost genes affect more than one phenotypic character.Pleiotropy:AlbinismA single defect in one of the enzymes catalyzing tyrosine to melanin can affect multiple phenotypic characters, from eye color to skin color to hair color.EpistasisA gene at one locus alters the phenotypic expression of a gene at a second locus.bb with dominant C alleleresults in brown mousePedigree AnalysisInformation about presence/absence of phenotypic trait is


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