Mendelian Genetics
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Mendelian Genetics

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Mendelian Genetics Presentation Transcript

  • 1. Mendelian Genetics How pea plants and humans mix it up
  • 2. Early Ideas About Heredity
    • People learned that it took two parents to make a baby
    • Many early beliefs about how characteristics are transmitted.
    • Blending theory
  • 3. Early Research
    • Mendel was not the first to perform experiments with pea plants
    • British farmers (stem height)
      • Performed almost the same experiments
      • Obtained the same results
      • Over 200 years before
    • T A Knight (flower color)
      • Same experiments
      • Same results
      • 1790’s
  • 4. Gregor Mendel
    • Born in 1822 in the Chech republic
    • Joined an Augustinian order in 1843
    • Flunked out of college, but made some great friends who showed him the value of good data
    • Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring
  • 5.  
  • 6. The Garden Pea Plant
    • Self-pollinating
    • True breeding (different alleles not normally introduced)
    • Can be experimentally cross-pollinated
  • 7. F 1 Results of One Monohybrid Cross
  • 8. F 2 Results of Monohybrid Cross
  • 9. Mendel’s Monohybrid Cross Results 787 tall 277 dwarf 651 long stem 207 at tip 705 purple 224 white 152 yellow 428 green 299 wrinkled 882 inflated 6,022 yellow 2,001 green 5,474 round 1,850 wrinkled F 2 plants showed dominant-to-recessive ratio that averaged 3:1
  • 10. Mendel’s Theory of Segregation
    • An individual inherits a unit of information (allele) about a characteristic from each parent
    • During gamete formation, the alleles segregate from each other
  • 11. Now we know about Alleles, alternative forms of a gene
  • 12. Punnett Square of a Monohybrid Cross Dominant phenotype can arise 3 ways, recessive only one Female gametes Male gametes A a A a Aa AA Aa aa
  • 13. Test Cross
    • Individual that shows dominant phenotype is crossed with individual with recessive phenotype
    • Examining offspring allows you to determine the genotype of the dominant individual
  • 14. Punnett Squares of Test Crosses Two phenotypes All dominant phenotype Homozygous recessive a a A a aa Aa Aa aa Homozygous recessive a a A A Aa Aa Aa Aa
  • 15. A Dihybrid Cross - F 1 Results AABB aabb x AaBb AB AB ab ab TRUE- BREEDING PARENTS: GAMETES : F 1 HYBRID OFFSPRING: purple flowers, tall white flowers, dwarf All purple-flowered, tall
  • 16. 16 Allele Combinations in F 2 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 A a B b aabb A abb aa B b AABB AABb A a BB A a Bb AAB b AA bb A a B b A abb A a B b aaBB aa B b A a BB 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 a B AB AB ab A b A b a B ab
  • 17. Explanation of Mendel’s Dihybrid Results
    • If the two traits are coded for by genes on separate chromosomes, sixteen gamete combinations are possible
    1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 A a B b aabb A abb aa B b AABB AABb A a BB A a Bb AAB b AA bb A a B b A abb A a B b aaBB aa B b A a BB 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 a B AB AB ab A b A b a B ab
  • 18. Phenotypic Ratios in F 2
    • Four Phenotypes:
      • Tall, purple-flowered (9/16)
      • Tall, white-flowered (3/16)
      • Dwarf, purple-flowered (3/16)
      • Dwarf, white-flowered (1/16)
    A a B b X A a B b
  • 19. Independent Assortment
    • Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait
    • Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis