Gregor Mendel – 1822-1884

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Mendelian Genetics. Gregor Mendel – 1822-1884. Asexual Reproduction. Bacteria can reproduce as often as every 12 minutes – and may go through 120 generations in one day Thus capable of producing 6 x 10 35 offspring per day Bacteria often produce 1 mutation per 1000 replications of DNA - PowerPoint PPT Presentation

Text of Gregor Mendel – 1822-1884

  • Gregor Mendel 1822-1884Mendelian Genetics

  • Asexual ReproductionBacteria can reproduce as often as every 12 minutes and may go through 120 generations in one dayThus capable of producing 6 x 1035 offspring per dayBacteria often produce 1 mutation per 1000 replications of DNASo for fast-growing species, mutation is a good way to respond to a changing environment

  • JohnMaynardSmithWhy Sex?

  • Sexual reproduction leads to genetic variation via:Independent assortment during meiosisCrossing over during meiosisRandom mixing of gametes (sperm and egg)

  • Independent Assortment

  • Prophase I of meiosisNonsister chromatids held together during synapsisPair of homologsChiasmaCentromereTEMAnaphase IAnaphase IIDaughter cellsRecombinant chromosomes

  • The random nature of fertilization adds to the genetic variation arising from meiosis.Any sperm can fuse with any egg.A zygote produced by a mating of a woman and man has a unique genetic identity.An ovum is one of approximately 8,388,608 possible chromosome combinations (223).The successful sperm represents one of 8,388,608 different possibilities (223).The resulting zygote is composed of 1 in 70 trillion (223 x 223) possible combinations of chromosomes. Crossing over adds even more variation to this.

  • Gregor Mendel 1822-1884Mendelian Genetics

  • Two possible types of inheritanceOne possible explanation of heredity is a blending hypothesisThe idea that genetic material contributed by two parents mixes in a manner analogous to the way blue and yellow paints blend to make greenAn alternative to the blending model is the particulate hypothesis of inheritance: the gene ideaParents pass on discrete heritable units, later known as genes

  • Mendels garden at Brunn (Brno) MonasteryMendels timeToday

  • Some genetic vocabulary

    Character: a heritable feature, such as flower colorTrait: a variant of a character, such as purple or white flowers

    Garden Pea

  • Flower Structure

  • Parental generation (P)StamensCarpelFirst filial generation offspring (F1)TECHNIQUERESULTS

  • In Mendels Experiments:Mendel chose to trackOnly those characters that varied in an either-or mannerMendel also made sure thatHe started his experiments with varieties that were true-breedingIn a typical breeding experimentMendel mated two contrasting, true-breeding varieties, a process called hybridization

  • Breeding TerminologyThe true-breeding parentsAre called the P (parental) generationThe hybrid offspring of the P generationAre called the F1 (filial) generationWhen F1 individuals self-pollinateThe F2 generation is produced

  • P GenerationEXPERIMENT(true-breeding parents)Purple flowersWhite flowers

  • P GenerationEXPERIMENT(true-breeding parents)F1 Generation (hybrids)Purple flowersWhite flowersAll plants had purple flowersSelf- or cross-pollination

  • P GenerationEXPERIMENT(true-breeding parents)F1 Generation (hybrids)F2 GenerationPurple flowersWhite flowersAll plants had purple flowersSelf- or cross-pollination705 purple- flowered plants224 white flowered plants

  • Mendel developed a hypothesis to explain his results that consisted of four ideasAlternative versions of genes (different alleles) account for variations in inherited charactersFor each character, an organism inherits two alleles, one from each parentIf two alleles differ, then one, the dominant allele, is fully expressed in the organisms appearance. The other, recessive allele has no effect on a hybrid organisms appearanceThe two alleles for each character segregate (separate) during gamete formation

  • Law of SegregationP GenerationAppearance:Genetic makeup:Gametes:Purple flowersWhite flowersPPppPp

  • Law of SegregationP GenerationF1 GenerationAppearance:Genetic makeup:Gametes:Appearance:Genetic makeup:Gametes:Purple flowersWhite flowersPurple flowersPpPPppPPpp1/21/2

  • Law of SegregationP GenerationF1 GenerationF2 GenerationAppearance:Genetic makeup:Gametes:Appearance:Genetic makeup:Gametes:Purple flowersWhite flowersPurple flowersSperm from F1 (Pp) plantPpPPppPPPPppppEggs from F1 (Pp) plantPPppPpPp1/21/23: 1

  • PhenotypePurplePurplePurpleWhite31112Ratio 3:1Ratio 1:2:1GenotypePP (homozygous)Pp (heterozygous)Pp (heterozygous)pp (homozygous)

  • Test crossDominant phenotype, unknown genotype: PP or Pp?Recessive phenotype, known genotype: ppPredictionsIf purple-flowered parent is PP If purple-flowered parent is Pp orSpermSpermEggsEggsorAll offspring purple1/2 offspring purple and 1/2 offspring whitePp Pp Pp Pp Pp Pp pp pp p p p p P P P p TECHNIQUERESULTS

  • P GenerationF1 GenerationPredictionsGametesEXPERIMENTRESULTSYYRRyyrryrYRYyRrHypothesis of dependent assortmentHypothesis of independent assortmentPredicted offspring of F2 generationSpermSpermorEggsEggsPhenotypic ratio 3:1Phenotypic ratio 9:3:3:1Phenotypic ratio approximately 9:3:3:1315108101321/21/21/21/21/41/41/41/41/41/41/41/49/163/163/161/16YRYRYRYRyryryryr1/43/4YrYryRyRYYRRYyRrYyRryyrrYYRRYYRrYyRRYyRrYYRrYYrrYyRrYyrrYyRRYyRryyRRyyRrYyRrYyrryyRryyrr

  • Segregation of alleles into eggsSegregation of alleles into spermSpermEggs1/21/21/21/21/41/41/41/4RrRrRRRRRRrrrrrr

  • Probability of YYRRProbability of YyRR1/4 (probability of YY)1/2 (Yy)1/4 (RR)1/4 (RR)1/161/8

  • Probability of YYRRProbability of YyRR1/4 (probability of YY)1/2 (Yy)1/4 (RR)1/4 (RR)1/161/8Probability of yyrr = ?A. 1/8B. 1/16C. 1/32

  • Probability of YYRRProbability of YyRR1/4 (probability of YY)1/2 (Yy)1/4 (RR)1/4 (RR)1/161/8Probability of YYrr = ?A. B. 1/8C. 1/16

  • Probability of YYRRProbability of YyRR1/4 (probability of YY)1/2 (Yy)1/4 (RR)1/4 (RR)1/161/8Probability of YxRr = ?(x can be Y or y)A. B. 3/4C. 3/8D. 1/16

  • Chance of at least two recessive traitsppyyRrppYyrrPpyyrrPPyyrrppyyrr1/4 (probability of pp) 1/2 (yy) 1/2 (Rr) 1/4 1/2 1/2 1/2 1/2 1/2 1/4 1/2 1/2 1/4 1/2 1/2 1/16 1/16 2/16 1/16 1/16 6/16 or 3/8

    *Figure 13.11 The results of crossing over during meiosis.*Figure 14.2 RESEARCH METHOD: Crossing Pea Plants*Figure 14.3 INQUIRY: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?*Figure 14.3 INQUIRY: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?

    *Figure 14.3 INQUIRY: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?

    *Table 14.1 The Results of Mendels F1 Crosses for Seven Characters in Pea Plants*Figure 14.5 Mendels law of segregation.*Figure 14.5 Mendels law of segregation.*Figure 14.5 Mendels law of segregation.*Figure 14.6 Phenotype versus genotype.*Figure 14.7 RESEARCH METHOD: The Testcross*Figure 14.8 INQUIRY: Do the alleles for one character assort into gametes dependently or independently of the alleles for a different character?*Figure 14.9 Segregation of alleles and fertilization as chance events.*Figure 14.UN01*Figure 14.UN01*Figure 14.UN01*Figure 14.UN01*Figure 14.UN02