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Gregor Mendel & Punnett Squares
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Gregor Mendel & Punnett Squares

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  • 1. 11.1-11.2 Gregor Mendel &Punnett Squares Pages 262 - 266 PD -old
  • 2. Goal 1 Describe how Mendel Studied inheritance in peas
  • 3.
    • Austrian Monk 1800’s
    • Taught High School
    • Managed monastery gardens
  • 4.
    • Pea plant observations
    • True-breeding plants
      • Self pollination = offspring identical to parents
  • 5.
    • Cross pollination used to study inheritance
      • Tall plant x short plant
      • Green seeds x yellow seeds
  • 6. Goal 2 Summarize Mendel’s conclusions about inheritance
  • 7.
    • Results of Mendel’s experiment
      • Cross pollination of true breeding parents (P)
      • Offspring (F1) only show one trait
      • No “blending” of traits
    Tall plant x short plant = all tall plants P P F1
  • 8.
    • Mendel’s 1 st conclusions about inheritance
      • Inheritance determined by factors passed from one generation to the next
      • Each trait determined by one gene that occurs in two different forms ( alleles )
      • Trait of height located on one gene as either short or tall alleles
  • 9. Goal 3 Explain the principle of dominance
  • 10.
    • He tried again with F1 generation
      • Cross pollination of F1 offspring
      • ¾ F2 offspring show one trait ¼ F2 show “hidden” trait
    F1 x F1 = F2 Tall plant x Tall plant = 3/4 tall plants ¼ short plants
  • 11. Creative commons Image credit: Madprime
  • 12.
    • Principle of dominance states:
    • some alleles are dominant and others are recessive
      • If dominant allele present, it will be expressed
      • Recessive alleles only expressed if NO dominant allele present
  • 13. Goal 4 Describe what happens to alleles during segregation in meiosis
  • 14.
    • Alleles separate during meiosis
    • Alleles segregate into one allele per gamete
    • Two types of gametes can be produced
    • Alleles pair up randomly when gametes unite during fertilization
  • 15.
    • Example on the board…
  • 16. Goal 5 Use Punnett Squares to: determine genotypic and phenotypic ratios of a cross to Predict outcomes
  • 17.
    • Phenotype = the expressed physical trait
      • What can be seen (brown hair)
      • Dependent on genotype
    • Genotype = the alleles of a genetic code
      • Genetic code (one maternal, one paternal)
        • Homozygous = alleles are the same (BB or bb)
        • Heterozygous = alleles are different (Bb)
  • 18.
    • Recessive phenotype
      • Genotype MUST be homozygous recessive
      • Genotype bb expresses phenotype blond hair
    • Dominant phenotype
      • Genotype may be homozygous dominant
        • BB expresses brown hair
      • Genotype may be heterozygous
        • Bb also expresses brown hair
  • 19.
    • Genotypes are used to create Punnett Squares and compare possible combinations of gametes
    • Parent 1 gamete possibilities
    • Parent 2 gamete possibilities
    Possible Combination Possible Combination Possible Combination Possible Combination
  • 20. B b b B Parent 1 : homozygous dominant Parent 2 : homozygous recessive Bb Bb Bb Bb
  • 21. B b B b Parent 1 : heterozygous Parent 2 : heterozygous bb Bb BB Bb
  • 22. B b B b Genotypic ratio of offspring 1BB : 2Bb : 1bb Phenotypic ratio of offspring 3 brown hair : 1 blond hair (75% chance) (25% chance) bb Blond hair Bb Brown hair BB Brown hair Bb Brown hair
  • 23. ? ? ? ? Parent 1 : heterozygous (Bb) Parent 2 : homozygous recessive (??) ?? ?? ?? ??
  • 24. B b b b Parent 1 : heterozygous (Bb) Parent 2 : homozygous recessive ( bb ) bb Bb Bb bb
  • 25. B b b b bb Bb Bb bb Genotypic ratio of offspring ?? : ?? Phenotypic ratio of offspring ?? : ??
  • 26. B b b b bb Bb Bb bb Genotypic ratio of offspring 2Bb : 2bb Phenotypic ratio of offspring 2 brown hair : 2 blond hair (50% chance) (50% chance)
  • 27.
    • Thanks to the following people who have generously shared images on Flickr creative commons:
    • Unertlkm… pea plant
    • Z e n… butterfly and pea bloom