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  • 1. Ch. 3 Section 1 The Work of Gregor Mendel
  • 2.
    • What comes to mind when you hear the
    • word inheritance?
    • Every living thing has a set of
    • characteristics inherited from its parents
    • Genetics - The study of heredity
  • 3. Gregor Mendel
    • Austrian monk
    • Studied biological inheritance
    • Studied math & science
    • Loved gardening
    • Mendel began conducting studies on the pea plants in the garden
  • 4. Fertilization
    • The female portion of the flower
    • produces egg cells
    • The male portion of the flower produces
    • sperm cells (in pollen)
    • When the egg and sperm join through
    • sexual reproduction, fertilization occurs!
  • 5.
    • Fertilization produces a new cell
    • Pea plants are usually self-pollinating
    • This means that sperm cells in pollen fertilize the egg cells of the same flower.
    • The seeds produces from by self-pollination only have ONE parent and therefore end up being identical to that parent!
    • Mendel referred to these types of pea plants as TRUE-BREEDING
  • 6.
    • True-Breeding
      • The new pea plants look exactly like the parent pea plants!
  • 7.
    • While Mendel did in fact study true-
    • breeding plants, he wanted to produce
    • seeds by joining male and female
    • reproductive cells from 2 DIFFERENT
    • plants
    • Meaning the egg from one plant and the
    • pollen from a different plant.
    • But how did he do this???
  • 8.
    • To prevent self-pollination, Mendel cut away
    • the male pollen bearing parts of the plant.
    • He then dusted the pollen from another plant
    • onto the flower
    • This process is called CROSS- POLLINATION
  • 9. Cross-Pollination
  • 10. Cross-Pollination
    • Produces plants that have 2 parents
    • This allowed Mendel to cross-breed
    • plants with different characteristics
    • He then studied the results…
  • 11. Genes & Dominance
    • Mendel studied 7 different pea plant traits
    • A trait is a specific characteristic such as flower
    • color or plant height
    • Each of the traits that Mendel studied had 2
    • contrasting forms
    • Example : tall vs. short
    • green seed vs. yellow seed
    • round seed vs. wrinkled seed
  • 12. Mendel’s Studies
    • Mendel crossed plants with each of the 7
    • contrasting forms.
    • He then studied their offspring...what did
    • they end up looking like?
    • Mendel referred to the parent plants (the
    • original ones used) as the P-Generation
    • The “P” stands for parental
  • 13.
    • The offspring from the P-Generation are
    • called the F 1 Generation
    • Or “First Filial” generation
    • In Latin, Filius or Filia means son or daughter
    • The offspring of crosses between parents
    • with different traits are called HYBRIDS
  • 14. So What Do the F 1 Hybrids Look Like???
    • Do the characteristics of the parents just
    • blend in the offspring?
    • NO!
    • To Mendel’s surprise, all of the offspring had
    • the character of only one of the parents!
    • The character of the other parent seemed to have disappeared….
  • 15. Mendel Drew 2 Conclusions
    • Biological inheritance is determined by factors that are passed from one generation to the next.
      • The chemical factors that determine these traits are called GENES
      • Each of the traits Mendel studied was controlled by a gene that occurred in 2 contrasting forms
      • These different contrasting forms are called ALLELES .
        • - The gene for plant height occurs in 2
        • forms…..tall alleles, short alleles
  • 16. 2 nd Conclusion
    • The Principle of Dominance
      • This states that some alleles are dominant and others are recessive.
      • An organism with a dominant allele for a particular trait will always exhibit that form of the trait.
  • 17.
    • An organism with a recessive allele for a
    • particular form of a trait will exhibit that
    • form ONLY when the dominant allele is not present.
    • In Mendel’s experiments,
      • The allele for tall plants was dominant and the allele for short plants was recessive
      • The allele for yellow seeds was dominant and the allele for green seeds was recessive.
  • 18. Segregation
    • So what happened to the recessive alleles…did they disappear in the F 1 generation?
    • To answer this question, Mendel allowed all 7 kinds of F 1 hybrid plants to produce and F 2 generation
    • The F 2 generation was produced through
    • self-pollination
    • ***remember this means that the egg
    • and sperm are from the same plant!
  • 19. The F 1 Cross
    • When Mendel compared the F 2 plants, he discovered that the traits controlled by the recessive alleles had reappeared!!!
    • Roughly 1/4 of the F 2 plants showed the recessive allele and the trait that went with it.
  • 20.  
  • 21. Why Did This Happen?
    • Mendel assumed that the dominant allele
    • had masked the recessive allele in the F 1
    • generation.
    • But there’s more to it…
    • The individual alleles actually separate
    • for each parent so that more
    • combinations are possible.
    • You don’t just get your mothers alleles or just your fathers alleles…you get a combination of the two.