Medels laws

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Medels laws

  1. 1. Gregor Mendel and his Laws of Inheritance
  2. 3. MENDEL’S LAWS OF HEREDITY <ul><li>I. WHY MENDEL SUCCEEDED </li></ul><ul><ul><li>Gregor Mendel – father of genetics </li></ul></ul><ul><ul><li>everything we know about genetics began with Mendel </li></ul></ul><ul><ul><li>He did the 1 st studies of heredity – the passing of characteristics to offspring </li></ul></ul><ul><ul><li>Genetics – study of heredity </li></ul></ul><ul><ul><li>The characteristics passed on called traits </li></ul></ul>
  3. 4. <ul><li>Traits - Specific characteristics that vary from one individual to another </li></ul><ul><li>Hybrids -The offspring of crosses between parents with different characteristics </li></ul><ul><li>Genes – portions of DNA that determine traits </li></ul><ul><li>Alleles - The different forms of a gene </li></ul>
  4. 5. 1. MENDEL CHOSE HIS SUBJECT CAREFULLY <ul><li>Used garden peas for his studies </li></ul><ul><li>Pea plants have male & female gametes (sex cells) </li></ul><ul><li>Male & female on same flower </li></ul><ul><li>He could control the fertilization process </li></ul><ul><li>Not many traits to keep track of </li></ul>
  5. 6. Mendel crossed the plants <ul><li>Fertilization - the uniting of male and female gametes (sex cells) </li></ul><ul><li>Cross - combining gametes from parents with different traits </li></ul>
  6. 7. For example: he crossed a purple-flowered plant with a white-flowered plant.
  7. 8. 2. MENDEL WAS A CAREFUL RESEARCHER <ul><li>USED CAREFULLY CONTROLLED EXPERIMENTS </li></ul><ul><li>STUDIED ONE TRAIT AT A TIME </li></ul><ul><li>KEPT DETAILED DATA </li></ul>
  8. 9. II. MENDEL’S MONOHYBRID CROSSES <ul><li>MENDEL STUDIED 7 TRAITS CAREFULLY </li></ul><ul><li>Mendel crossed plants w/ different traits to see what traits the offspring would have </li></ul><ul><li>These offspring are called hybrids – (offspring of parents w/ different traits) </li></ul><ul><li>A monohybrid cross is one that looks at only one trait (let’s look at plant height – tall or short) </li></ul>
  9. 10. Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results.
  10. 11. A. THE 1 ST GENERATION <ul><li>Mendel crossed two plants – 1 tall & 1 short (they came from tall & short populations) </li></ul><ul><li>These plants are called the parent generation ( P generation ) </li></ul><ul><li>The offspring were all called the 1 st filial generation ( F 1 generation ) </li></ul><ul><li>All the offspring were tall (the short plants were totally excluded) </li></ul>
  11. 12. Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants. Mendel’s cross between tall pea plants and small pea plants yielded all tall pea plants. X = x = X = F 1 GENERATION P GENERATION
  12. 13. B. THE 2 ND GENERATION <ul><li>Next, Mendel crossed two plants from the F 1 generation </li></ul><ul><li>The offspring from this cross are called the 2 nd filial generation ( F 2 GENERATION ) </li></ul><ul><li>Mendel found that ¾ of the offspring were tall & ¼ were short (the short plants reappeared!!!!!!) </li></ul>
  13. 14. Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small. F 2 GENERATION x =
  14. 15. OR ANOTHER TRAIT: FLOWER COLOR
  15. 17. TO GO ANY FURTHER, WE MUST UNDERSTAND ALLELES, DOMINANCE, & SEGREGATION <ul><li>Genes – a section of DNA that codes for one protein </li></ul><ul><ul><li>These genes are what control & produce traits </li></ul></ul><ul><li>The genes Mendel studied came in two forms (tall/short - round/wrinkled - yellow/green…….etc.) </li></ul><ul><li>Alternate forms of a gene are called alleles </li></ul><ul><li>Alleles are represented by a one or two letter symbol (e.g. T for tall, t for short) </li></ul>
  16. 19. ALLELES CONT’D <ul><li>THESE 2 ALLELES ARE NOW KNOWN TO BE FOUND ON COPIES OF CHROMOSOMES – ONE FROM EACH PARENT </li></ul>
  17. 20. THE RULE OF DOMINANCE <ul><li>A dominant trait is the trait that will always be expressed if at least one dominant allele is present </li></ul><ul><li>The dominant allele is always represented by a capital letter </li></ul><ul><li>A recessive trait will only be expressed if both alleles are recessive </li></ul><ul><li>Recessive traits are represented by a lower case letter </li></ul>
  18. 21. <ul><li>BY CONVENTION when choosing a letter to represent the alleles: </li></ul><ul><li>The dominant trait is given a capitol letter, the lowercase of that same letter is the recessive trait.  DO NOT MIX LETTERS.  Pick one and stick to it. </li></ul><ul><li>Also, some letters are better than others.  Capital S looks a lot like a lowercase (s).  Pick a different letter... </li></ul><ul><li>   Okay                                                   Better (use H for hair) </li></ul><ul><li>Short  hair  = SS                                    HH </li></ul><ul><li>Short hair = Ss                                       Hh </li></ul><ul><li>Long hair = ss                                        hh  </li></ul>
  19. 22. DOMINANCE CONT’D <ul><li>LET’S USE TALL & SHORT PEA PLANTS FOR AN EXAMPLE </li></ul><ul><li>WHICH OF THESE WILL SHOW THE DOMINANT & RECESSIVE TRAIT? </li></ul>TT Tt tt DOMINANT TRAIT RECESSIVE TRAIT
  20. 23. Practice picking letters.... the following traits are found in the common Shirtus americanus . <ul><li>Polka dots are dominant to stripes. </li></ul><ul><li>Long sleeves are dominant to short sleeves. </li></ul><ul><li>Collared shirts are recessive. </li></ul><ul><li>Buttons are dominant over snaps. </li></ul><ul><li>Pockets are recessive.    </li></ul>
  21. 24. <ul><li>When an organism is studied for three different genes and has the alleles AABbCC, it is homozygous for A and C genes but heterozygous for the B gene. </li></ul>A = antenna a = no antenna B = black b = purple C = chompers c = no chompers So what would this organism look like?
  22. 25. THE LAW OF SEGREGATION <ul><li>MENDEL ASKED HIMSELF……..”HOW DID THE RECESSIVE SHORT PLANTS REAPPEAR IN THE F2 GENERATION?” </li></ul><ul><li>HE CONCLUDED THAT EACH TALL PLANT FROM THE F1 GENERATION CARRIED TWO ALLELES, 1 DOMINANT TALL ALLELE & ONE RECESSIVE SHORT ALLELE </li></ul><ul><li>SO ALL WERE Tt </li></ul>
  23. 26. SEGREGATION CONT’D <ul><li>HE ALSO CONCLUDED THAT ONLY ONE ALLELE FROM EACH PARENT WENT TO EACH OFFSPRING </li></ul><ul><li>HIS CORRECT HYPOTHESIS WAS THAT SOMEHOW DURING FERTILIZATION, THE ALLELES SEPARATED (SEGREGATED) & COMBINED WITH ANOTHER ALLELE FROM THE OTHER PARENT </li></ul><ul><li>The law of segregation states that during gamete formation, the alleles separate to different gametes </li></ul>
  24. 27. F1 GENERATION FATHER MOTHER T t T t T T T t t t F2 GENERATION - the law of dominance explained the heredity of the offspring of the f1 generation - the law of segregation explained the heredity of the f2 generation
  25. 30. PHENOTYPES & GENOTYPES <ul><li>PHENOTYPE – THE WAY AN ORGANISM LOOKS AND BEHAVES – ITS PHYSICAL CHARACTERISTICS (i.e. – TALL, GREEN, BROWN HAIR, BLUE EYES, ETC.) </li></ul><ul><li>GENOTYPE – THE GENE COMBONATION (ALLELIC COMBINATION) OF AN ORGANISM – (i.e. – TT, Tt, tt, ETC.) </li></ul><ul><ul><li>HOMOZYGOUS – 2 ALLELES ARE THE SAME </li></ul></ul><ul><ul><li>HETEROZYGOUS – 2 ALLELES DIFFERENT </li></ul></ul>

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