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Mendel and heredity
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Mendel and heredity


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  • 1. Mendel and Heredity
    • 7-1 Fundamental of Genetics
    • 7-2 Analyzing Heredity
    • 7-3 Human Genetics
  • 2. Fundamentals of Genetics
    • List four characteristics that make Pisum sativum a good subject for genetic studies.
    • Outline the three major steps of Gregor Mendel’s garden pea experiments.
    • Explain how Mendel derived ratios from his observations.
    • Compare and contrast Mendel’s two laws of heredity.
  • 3. Gregor Mendel
    • Began experiments in 1857
    • Austrian monk
    • Studied genetics of peas
    • Father of genetics
    • Failed his math/science teacher exam
    • Attended Univ. of Vienna - experimentation
  • 4. Why the Garden Pea?
    • Many varieties – 32 to start – used 7
    • More than one form of the same trait
    • Small, easy to grow, matures quickly, large numbers of offspring…
    • Ability to cross-pollinate and self-pollinate
  • 5. Experimental Design
    • Step 1 – allow self-pollination to produce plants that are true-breeding. P generation.
    • Step 2 – cross-pollination. F1 generation.
    • Step 3 – self-pollination of F1 generation. F2 generatoin.
  • 6. Two ratios observed
    • Dominant trait – expressed trait in F1 generation.
    • Recessive trait – not expressed in F1 generation.
    • Self-pollination of F1 yields a 3:1 phenotypic ratio, but a 1:2:1 genotypic ratio.
  • 7. Mendel’s proposed Theory
    • Parent’s pass factors(genes) to their offspring that produce traits.
    • Two alleles for each trait – heterozygous (Tt) or homozygous (TT, tt)
    • Phenotype = physical appearance
    • Genotype = set of alleles
    • Dominant is expressed over recessive
  • 8. Mendel’s Laws
    • Law of segregation – member of each pair of alleles are separated when gametes are formed.
    • Law of Independent Assortment – pairs of alleles separate independently of one another during gamete formation.
  • 9. Interpreting Mendel’s Model
    • Capital letters= dominant alleles
    • Lower case letters = recessive alleles
    • Two alleles for each trait
    • Homozygous dominant = DD
    • Heterozygous dominant = Dd (hybrid)
    • Homozygous recessive - dd
  • 10. Probability
    • The likelihood that an event will take place.
    • = number of one kind of possible outcome
    • total number of possible outcomes
  • 11. Monohybrid Crosses
    • Provide information about one pair of contrasting traits.
  • 12. Dihybrid Crosses
    • Involve two pairs of contrasting traits.
  • 13.  
  • 14. Review Questions:
    • Write the formula used to determine the likelihood that an event will occur. How is probability used in genetics?
    • Construct a Punnett Square to predict the outcome of a monohybrid cross between two heterozygous tall pea plants. What are the expected phenotypic and genotypic ratios?
    • What is a dihybrid cross? What is the expected phenotypic ratio for a heterozygous dihybrid cross?
  • 15. 5 Factors that Influence Heredity
    • A trait is displayed that is intermediate between two parents.
    • Flower color in snapdragons
      • Red + White = Pink
    #1 Incomplete Dominance
  • 16. #2 Codominance
    • Two dominant alleles are expressed simultaneously
    • Different from incomplete dominance because both traits are displayed
    • Example) roan coat in horses is a result of a cross between a homozygous red and homozygous white horse…resulting in a horse with a coat of red and white hair.
  • 17. #3 Multiple Alleles
    • Genes with more than one allele
    • Example) three alleles can determine
    • blood type (A, B, and O)
      • A and B are dominant over O
      • Neither A nor B are dominant over each other
      • When A and B are present…they are codominant
  • 18. #4 Continuous Variation
    • Several genes influence a trait
    • Examples) height and weight
    • A variety of phenotypes exist from one extreme to another
  • 19. #5 Environmental Influences
    • Phenotypes being influenced by the environment
    • Example) the coat color of the arctic fox in winter
  • 20. Review Questions
    • What are dominant and recessive alleles?
    • Why were true-breeding plants important in Mendel’s experiments?
    • What is a Punnett Square?
    • What is the difference between Phenotype and Genotype?
    • Describe two inheritance patterns besides simple dominance.