Mendel and heredity


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Mendel and heredity

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