Mendelian Genetics


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Mendelian Genetics

  1. 1. Inheritance: Mendelian Genetics I. Gregor Mendel (1865) A. Before Mendel B. Mendel’s experimental approach II. Genetic terms 1. genes 2. gene pair 3. alleles 4. homozygous/heterozygous 5. dominant/recessive 6. homozygous dominant and recessive/heterozygous 7. genotype/phenotype III. Genetic crosses A. Monohybrid crosses B. Dihybrid crosses IV. Mendel's discoveries A. Principle of segregation B. Principle of independent assortment C. Genes are particles
  2. 2. A. Before Mendel The blending theory (paradigm) Inheritance of acquired characteristics <ul><li>statistics </li></ul><ul><li>amateur </li></ul><ul><li>inductive leap </li></ul>Darwin and Mendel
  3. 3. B. Mendel’s experimental approach Hermaphrodite Perfect flowers pollen egg Genetic barriers
  4. 4. Pea plant traits
  5. 5. Pure breeding lines Breed true
  6. 6. <ul><li>Why was Mendel’s experimental findings ignored during </li></ul><ul><li>his lifetime? </li></ul><ul><li>He was an amateur </li></ul><ul><li>There was a problem with inductive leaps </li></ul><ul><li>The dominant paradigm was opposed to his findings </li></ul><ul><li>He used statistics </li></ul><ul><li>All of the above </li></ul>
  7. 7. II. Genetic terms 1. genes/ loci 2. gene pair = homologues 3. alleles 4. homozygous/heterozygous 5. dominant/recessive 6. homozygous dominant and recessive/heterozygous 7. genotype/phenotype
  8. 8. Human traits Hand folding
  9. 9. III. Genetic crosses Punnett Square
  10. 10. III. Genetic crosses
  11. 11. Red coat in foxes is a dominant trait; white is the recessive trait. If a red fox whose mother had a white coat is bred to a white fox, what will be the probable percentage of red kits (baby foxes)? a. 25% b. 50% c. 75% d. 100%
  12. 12. <ul><li>Monohybrid cross: genetic disorders and lethal genes </li></ul>
  13. 14. <ul><li>Tay-Sachs is a lethal disorder resulting in death by the </li></ul><ul><li>age of 4. A couple who are normal have a child with Tay- </li></ul><ul><li>Sachs. Which of the following is true of the parents? </li></ul><ul><li>One parent is homozygous dominant and the other is </li></ul><ul><li>homozygous recessive </li></ul><ul><li>b. both parents are heterozygous </li></ul><ul><li>c. both parents are homozygous dominant </li></ul><ul><li>d. both parents are homozygous recessive </li></ul>
  14. 15. Sickle cell trait: recessive disorder
  15. 16. Sickle cell trait: recessive disorder Homozygous dominant = normal, not malaria resistant Heterozygous = malaria resistant Homozygous recessive = sickle cell anemia
  16. 17. Huntington’s disease: dominant disorder CAGCAGCAG Normal, 26 times HD, 40 to >100 times Manifests after age 40 Why is dominant lethality less common than recessive?
  17. 18. Dwarfism : dominant trait Homozygous dominant = lethal Heterozygous = dwarf Homozygous recessive = normal height Hardy-Weinburg rule
  18. 19. If two achondroplasic dwarfs have children, what fraction of the children would be expected to be dwarfs like their parents? a. 1/4 b. 1/2 c. 2/3 d. 3/4 <ul><li>What determines how common a trait is in a population? </li></ul><ul><li>it’s frequency </li></ul><ul><li>Dominance </li></ul><ul><li>Selection </li></ul><ul><li>Chance </li></ul>
  19. 20. B. Dihybrid crosses: Human traits Dimples dominant to no dimples Brown eyes dominant to blue Dark hair dominant to light hair Curly hair incompletely dominant to straight hair
  20. 21. In humans, a widow's peak is dominant and a straight hairline is recessive. Dimples are dominant and no dimples are recessive. A male who is heterozygous for both widow's peak and dimples has a child with a woman who has a straight hairline and no dimples. What is the phenotype ratio of children can they produce? a. 3: 1 b. 2:2 c. 1:1:1:1 d. 4:0
  21. 22. IV. Mendel’s discoveries A. Principle of segregation Sexually reproducing diploid organisms have 2 alleles of each gene. These 2 alleles segregate from each other to form gametes that contain only 1 allele of each gene.
  22. 23. B. Principle of independent assortment Different genes on different chromosomes segregate into gametes independently of each other.
  23. 24. C. Genes are particles
  24. 25. V. Eugenics Francis Galton Social Darwinism Positive Eugenics
  25. 26. Eugenics
  26. 27. Eugenics
  27. 28. Eugenics today? IVF/ PGD Gene “therapy”
  28. 29. The end