Gregor Mendel Pea Plants and Inheritance Patterns

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  • Gregor MendelPea Plants and Inheritance Patterns

  • Who is Gregor Mendel?Mendel was born in 1822 in AustriaHis father was a peasant farmer, tenanted to a local aristocrat who was very interested in scientific crop improvementThe family was very poorMendels early education was with local priest and teacherShowed considerable academic capability and so was sent to larger town with more opportunitiesFinancial problems plagued him, affecting his health, so Mendel decided to enter monastery as means of support

  • At the Monastery

  • At the MonasteryMendel taught 6th and 7th grade age children He also had access to the monasterys libraryFr. Napp, head of the monastery, had a shared interest in botany and agriculture

  • Mendels Garden

  • Mendels Model Organism

    The Garden PeaSelf-FertilizingMatured QuicklySeveral Easily Identifiable Traits

    Used Consistent Methods:

    Opened flower & placedpollen from one type ontothe stigma

  • Pea Plant CharacteristicsSeed ShapeSeed ColorPod ShapePod ColorFlower ColorFlower PositionStem Length

  • Mendels First ExperimentCrossed Pure Tall Pea Plant (TT) x Pure Short (Dwarf) Pea Plant (tt)

    Hypothesis:The offspring would be:All tallAll shortAll intermediateSome would be talls and some short

  • The Results?1st Experiment: Crossed Pure Tall x Pure ShortAll offspring (F1) tall2nd Experiment: Bred F1Ratio of 787 tall to 277 short (3:1)Similar to chance events from flipping 2 pairs of coins

  • A cross between individuals differing in single character is a monohybrid cross.The analysis of monohybrid crosses allowed Mendel to deduce the Law of SegregationGenes come in pairs that separate in the formation of sex cells (and these sex cells unite randomly at fertilization).Monohybrid Crosses and the Law of Segregation

  • Staying the Course Crosses to the F2 (The Grandchildren)The reappearance of the recessive trait in of the F2, suggests genes come in pairs that separate in the formation of sex cells.Crossed one of the F1 tall plants with its dwarf parent: F1 Tall x DwarfPossible Outcomes:All would be tallMixture of Tall & DwarfAll would be intermediateExperimental results

  • Therefore, the Law of Segregation indeed is a general principle of genetics.Monohybrid Crosses are Consistent!

  • Mendels Experiments The Next GenerationMendel recognized that it is not always possible to tell what offspring will be like by inspecting the parent

    Mendel could test if tall plants were pure-breeds (homozygotes) or hybrid (heterozygotes) by the back-cross or test-cross

    What % would you predict for each genotype?Tt t tTtt t

  • Mendels Hypothesis

  • Mendels HypothesisThere are alternative forms for genes, the units that determine inheritable characteristics (AA or Aa or aa)For each inherited characteristic, an organism has two alleles, one inherited from each parent. A sperm or egg carries only one allele (A or a)for each inherited characteristic, because allele pairs separate from each other during meiosis. At fertilization, the sperm and egg unite and restore the gene to the paired condition. When the two alleles of a pair are different, one is fully expressed (dominant) and the other is completely masked (recessive). The members of the pair may be identical (homozygous) or non-identical (heterozygous).

  • The alignment of one pair of homologs is independent of any other.Principle of Independent Assortment: The assortment of one pair of genes into gametes is independent of the assortment of another pair of genes.Revisiting Meiosis

  • Incomplete DominanceIncomplete dominance is a blending of colorsDominance relationships may differ, but the Principle of Segregation is the same

  • Polygenic Inheritance:When a Single Trait is Influenced by Many Genes

  • Multiple AllelesMany genes are present in three or more versions (alleles) this is multiple allelesThe human ABO blood group is determined by three alleles (IA, IB, and I) of a single gene

  • CodominanceThe human ABO blood group also exhibits codominance another genetic phenomenonCodominance occurs when the phenotype associated with each allele is expressed in the heterozygoteThe AB phenotype (genotype IA IB) is an example of codominance

  • Genetics of Blood Types

    PhenotypeGenotypeAntigen on RBCAntibodies in BloodDonation StatusAA A or A itype A antigens on surface of RBCanti-B antibodies__BBB or B itype B antigens on surface of RBCanti-A antibodies__ABABboth type A & type B antigens on surface of RBCno antibodiesuniversal recipientOi ino antigens on surface of RBCanti-A & anti-B antibodiesuniversal donor

  • Sex-Linked TraitsXHXHXHXh2 normal parents,but mother is carrierx

  • Sex-Linked TraitsSex chromosomes have other genes on them, especially the X chromosomeHemophilia in humansBlood doesnt clotDuchenne muscular dystrophy in humansLoss of muscle controlRed-green color blindnessSee green & red as shades of grey

  • Polydactyly Individuals are born with extra fingers and toesThe allele for 6+ fingers and toes is dominant,while the allele for 5 digits is recessiveRecessive is far more common! (1:500 have polydactyly)

  • Mendel performed dihybrid crosses to find out.Are Different Characters Like Color and Shape Inherited Together or Inherited Independently?

  • Note that were simultaneously applying the Principles of Segregations and Independent Assortment. Dihybrid Crosses

    Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010Mendelian GeneticsG. Podgorski, Biol 1010