1 Mendelelian Genetics copyright cmassengale. 2 Gregor Mendel ( 1822-1884) Responsible for the Laws governing Inheritance of Traits copyright cmassengale

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1Mendelelian Geneticscopyright cmassengale2

Gregor Mendel(1822-1884)Responsible for the Laws governing Inheritance of Traitscopyright cmassengale3Gregor Johann MendelAustrian monkStudied the inheritance of traits in pea plantsDeveloped the laws of inheritanceMendel's work was not recognized until the turn of the 20th century

copyright cmassengale4Gregor Johann MendelBetween 1856 and 1863, Mendel cultivated and tested some 28,000 pea plantsHe found that the plants' offspring retained traits of the parentsCalled the Father of Genetics"

copyright cmassengale6Mendel stated that physical traits are inherited as particlesMendel did not know that the particles were actually Chromosomes & DNAParticulate Inheritance

copyright cmassengale7Genetic TerminologyTrait - any characteristic that can be passed from parent to offspring Heredity - passing of traits from parent to offspring Genetics - study of heredity copyright cmassengale8Types of Genetic CrossesMonohybrid cross - cross involving a single traite.g. flower color Dihybrid cross - cross involving two traits e.g. flower color & plant heightcopyright cmassengale9Punnett SquareUsed to help solve genetics problems

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copyright cmassengale11Designer GenesAlleles - two forms of a gene (dominant & recessive) Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R) Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r) copyright cmassengale12More TerminologyGenotype - gene combination for a trait (e.g. RR, Rr, rr) Phenotype - the physical feature resulting from a genotype (e.g. red, white) copyright cmassengale13Genotype & Phenotype in FlowersGenotype of alleles:R = red flowerr = yellow flowerAll genes occur in pairs, so 2 alleles affect a characteristicPossible combinations are:GenotypesRR RrrrPhenotypesRED RED YELLOW

copyright cmassengale14GenotypesHomozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure Heterozygous genotype - gene combination of one dominant & one recessive allele (e.g. Rr); also called hybridcopyright cmassengale21Eight Pea Plant TraitsSeed shape --- Round (R) or Wrinkled (r)Seed Color ---- Yellow (Y) or Green (y)Pod Shape --- Smooth (S) or wrinkled (s)Pod Color --- Green (G) or Yellow (g)Seed Coat Color ---Gray (G) or White (g)Flower position---Axial (A) or Terminal (a)Plant Height --- Tall (T) or Short (t)Flower color --- Purple (P) or white (p)copyright cmassengale22

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copyright cmassengale28Monohybrid Crossescopyright cmassengale29Trait: Seed ShapeAlleles: R Roundr WrinkledCross: Round seeds x Wrinkled seedsRR x rrP1 Monohybrid CrossRRrrRrRrRrRrGenotype: RrPhenotype: RoundGenotypicRatio: All alikePhenotypicRatio: All alikecopyright cmassengale30P1 Monohybrid Cross ReviewHomozygous dominant x Homozygous recessiveOffspring all Heterozygous (hybrids)Offspring called F1 generationGenotypic & Phenotypic ratio is ALL ALIKEcopyright cmassengale31Trait: Seed ShapeAlleles: R Roundr WrinkledCross: Round seeds x Round seedsRr x RrF1 Monohybrid CrossRrrRRRrrRrRrGenotype: RR, Rr, rrPhenotype: Round & wrinkledG.Ratio: 1:2:1P.Ratio: 3:1copyright cmassengale32F1 Monohybrid Cross ReviewHeterozygous x heterozygousOffspring:25% Homozygous dominant RR50% Heterozygous Rr25% Homozygous Recessive rrOffspring called F2 generationGenotypic ratio is 1:2:1Phenotypic Ratio is 3:1copyright cmassengale33

What Do the Peas Look Like?copyright cmassengale34And Now the Test CrossMendel then crossed a pure & a hybrid from his F2 generationThis is known as an F2 or test crossThere are two possible testcrosses:Homozygous dominant x HybridHomozygous recessive x Hybridcopyright cmassengale35Trait: Seed ShapeAlleles: R Roundr WrinkledCross: Round seeds x Round seedsRR x RrF2 Monohybrid Cross (1st)RRrRRRRrRRRrGenotype: RR, RrPhenotype: RoundGenotypicRatio: 1:1PhenotypicRatio: All alikecopyright cmassengale36Trait: Seed ShapeAlleles: R Roundr WrinkledCross: Wrinkled seeds x Round seedsrr x RrF2 Monohybrid Cross (2nd)rrrRRrrrRrrrGenotype: Rr, rrPhenotype: Round & WrinkledG. Ratio: 1:1P.Ratio: 1:1copyright cmassengale37F2 Monohybrid Cross ReviewHomozygous x heterozygous(hybrid)Offspring:50% Homozygous RR or rr50% Heterozygous RrPhenotypic Ratio is 1:1Called Test Cross because the offspring have SAME genotype as parentscopyright cmassengale38Practice Your CrossesWork the P1, F1, and both F2 Crosses for each of the other Seven Pea Plant Traitscopyright cmassengale39Mendels Lawscopyright cmassengale40Results of Monohybrid CrossesInheritable factors or genes are responsible for all heritable characteristics Phenotype is based on Genotype Each trait is based on two genes, one from the mother and the other from the father True-breeding individuals are homozygous ( both alleles) are the samecopyright cmassengale41Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.All the offspring will be heterozygous and express only the dominant trait.RR x rr yields all Rr (round seeds)

copyright cmassengale42Law of Dominance

copyright cmassengale43Law of SegregationDuring the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. copyright cmassengale44Applying the Law of Segregation

copyright cmassengale45Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This law can be illustrated using dihybrid crosses.copyright cmassengale46Dihybrid CrossA breeding experiment that tracks the inheritance of two traits.Mendels Law of Independent Assortmenta. Each pair of alleles segregates independently during gamete formationb. Formula: 2n (n = # of heterozygotes)copyright cmassengale47Question:How many gametes will be produced for the following allele arrangements?Remember: 2n (n = # of heterozygotes)



3.MmNnOoPPQQRrssTtQqcopyright cmassengale48Answer:1. RrYy: 2n = 22 = 4 gametesRY Ry rY ry

2. AaBbCCDd: 2n = 23 = 8 gametesABCD ABCd AbCD AbCdaBCD aBCd abCD abCD

3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametescopyright cmassengale49Dihybrid CrossTraits: Seed shape & Seed colorAlleles: R round r wrinkled Y yellow y green RrYy x RrYyRY Ry rY ryRY Ry rY ryAll possible gamete combinationscopyright cmassengale50Dihybrid CrossRYRyrYryRYRyrYrycopyright cmassengale51Dihybrid CrossRRYYRRYyRrYYRrYyRRYyRRyyRrYyRryyRrYYRrYyrrYYrrYyRrYyRryyrrYyrryyRound/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 19:3:3:1 phenotypic ratioRYRyrYryRYRyrYrycopyright cmassengale

53Test CrossA mating between an individual of unknown genotype and a homozygous recessive individual.Example: bbC__ x bbcc

BB = brown eyesBb = brown eyesbb = blue eyes

CC = curly hairCc = curly haircc = straight hairbCb___bccopyright cmassengale54Test CrossPossible results:bCb___bcbbCcbbCcCbCb___bcbbCcbbccorccopyright cmassengale55Summary of Mendels lawsLAWPARENT CROSSOFFSPRINGDOMINANCETT x tt tall x short100% Tt tallSEGREGATIONTt x Tt tall x tall75% tall 25% shortINDEPENDENT ASSORTMENTRrGg x RrGg round & green x round & green9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow podscopyright cmassengale56Incomplete DominanceandCodominancecopyright cmassengale57Incomplete DominanceF1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties.Example: snapdragons (flower)red (RR) x white (rr)

RR = red flowerrr = white flowerRRrrcopyright cmassengale58Incomplete DominanceRrRrRrRrRRrAll Rr = pink(heterozygous pink)produces theF1 generationrcopyright cmassengale59Incomplete Dominance

copyright cmassengale60CodominanceTwo alleles are expressed (multiple alleles) in heterozygous individuals.Example: blood type

1.type A= IAIA or IAi2.type B= IBIB or IBi3.type AB= IAIB4.type O= iicopyright cmassengale61Codominance ProblemExample:homozygous male Type B (IBIB)x heterozygous female Type A (IAi)IAIBIBiIAIBIBi1/2 = IAIB1/2 = IBi IBIAiIBcopyright cmassengale62Another Codominance ProblemExample: male Type O (ii) x female type AB (IAIB)IAiIBiIAiIBi1/2 = IAi1/2 = IBi iIAIBicopyright cmassengale63CodominanceQuestion:If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents?

boy - type O (ii) X girl - type AB (IAIB)copyright cmassengale64CodominanceAnswer:IAIBiiParents:genotypes = IAi and IBiphenotypes = A and BIBIAiicopyright cmassengale65Sex-linked TraitsTraits (genes) located on the sex chromosomesSex chromosomes are X and YXX genotype for femalesXY genotype for malesMany sex-linked traits carried on X chromosomecopyright cmassengale66Sex-linked TraitsSex ChromosomesXX chromosome - femaleXy chromosome - malefruit flyeye colorExample: Eye color in fruit fliescopyright cmassengale67Sex-linked Trait ProblemExample: Eye color in fruit flies (red-eyed male) x (white-eyed female) XRY x XrXrRemember: the Y chromosome in males does not carry traits.RR = red eyedRr = red eyedrr = white eyedXY = maleXX = femaleXRXr XrYcopyright cmassengale68Sex-linked Trait Solution:XR XrXr YXR XrXr Y50% red eyed female50% white eyed maleXRXr XrYcopyright cmassengale69Female Carrie


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