Mendel and heredity
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Mendel and heredity






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    Mendel and heredity Mendel and heredity Presentation Transcript

    • Mendel and Heredity
      • 7-1 Fundamental of Genetics
      • 7-2 Analyzing Heredity
      • 7-3 Human Genetics
    • 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.
    • 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
    • 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
    • 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.
    • 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.
    • 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
    • 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.
    • 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
    • Probability
      • The likelihood that an event will take place.
      • = number of one kind of possible outcome
      • total number of possible outcomes
    • Monohybrid Crosses
      • Provide information about one pair of contrasting traits.
    • Dihybrid Crosses
      • Involve two pairs of contrasting traits.
    • 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?
    • 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
    • #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.
    • #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
    • #4 Continuous Variation
      • Several genes influence a trait
      • Examples) height and weight
      • A variety of phenotypes exist from one extreme to another
    • #5 Environmental Influences
      • Phenotypes being influenced by the environment
      • Example) the coat color of the arctic fox in winter
    • 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.