Ch.3 1 Pp2


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Ch.3 1 Pp2

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