Genetics                     &             The Work of MendelAP Biology
Gregor Mendel  Modern genetics began in the    mid-1800s in an abbey garden,    where a monk named Gregor    Mendel docum...
Mendel’s work                    Pollen transferred from white                                    flower to stigma of purp...
Mendel collected data for 7 pea traitsAP Biology
Looking closer at Mendel’s work               true-breeding       true-breeding                                X white-flo...
What did Mendel’s findings mean?    Traits come in alternative versions        purple vs. white flower color        all...
Traits are inherited as discrete units     For each characteristic, an organism        inherits 2 alleles, 1 from each pa...
What did Mendel’s findings mean?     Some traits mask others            purple & white flower colors are             I’l...
Genotype vs. phenotype     Difference between how an organism        “looks” & its genetics            phenotype        ...
Making crosses     Can represent alleles as letters          flower color alleles → P or p          true-breeding purpl...
Looking closer at Mendel’s work               true-breeding       true-breeding                                X white-flo...
Aaaaah,                                phenotype & genotype     Punnett squares             can have differentF1          ...
Genotypes     Homozygous = same alleles = PP, pp     Heterozygous = different alleles = Pp             homozygous       ...
Phenotype vs. genotype     2 organisms can have the same        phenotype but have different genotypes                 pu...
Test cross     Breed the dominant phenotype —        the unknown genotype — with a        homozygous recessive (pp) to   ...
How does a Test cross work?                   x                    x             PP        pp        Pp           pp      ...
Mendel’s 1st law of heredity PP                                                        P     Law of segregation         ...
Law of Segregation     Which stage of        meiosis creates the        law of segregation?                     Metaphase...
Monohybrid cross     Some of Mendel’s experiments followed        the inheritance of single characters          flower c...
Dihybrid cross    Other of Mendel’s       experiments followed       the inheritance of 2       different characters     ...
Dihybrid cross            true-breeding                         true-breedingP        yellow, round peas                  ...
What’s going on here?     If genes are on different chromosomes…          how do they assort in the gametes?          t...
YyRr            YyRr                                      or   Is this the way it works?                            YR   y...
YyRr              YyRr                                              or   Dihybrid cross                                  Y...
Can you think                                                        of an exception     Mendel’s 2nd law of heredity     ...
Law of Independent Assortment     Which stage of meiosis        creates the law of        independent assortment?  Rememb...
The   chromosomal   basis of Mendel’s   laws…   Trace the genetic   events through   meiosis, gamete   formation &   ferti...
Review: Mendel’s laws of heredity      Law of segregation            monohybrid cross              single trait        ...
Mendel chose peas wisely    Pea plants are good for genetic research            available in many varieties with distinc...
Mendel chose peas luckily     Pea plants are good for genetic research            relatively simple genetically         ...
Any Questions??AP Biology
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  • He studied at the University of Vienna from 1851 to 1853 where he was influenced by a physicist who encouraged experimentation and the application of mathematics to science and a botanist who aroused Mendel’s interest in the causes of variation in plants. After the university, Mendel taught at the Brunn Modern School and lived in the local monastery. The monks at this monastery had a long tradition of interest in the breeding of plants, including peas. Around 1857, Mendel began breeding garden peas to study inheritance.
  • P = parents F = filial generation
  • In a typical breeding experiment, Mendel would cross-pollinate ( hybridize ) two contrasting, true-breeding pea varieties. The true-breeding parents are the P generation and their hybrid offspring are the F 1 generation . Mendel would then allow the F 1 hybrids to self-pollinate to produce an F 2 generation.
  • In a typical breeding experiment, Mendel would cross-pollinate ( hybridize ) two contrasting, true-breeding pea varieties. The true-breeding parents are the P generation and their hybrid offspring are the F 1 generation . Mendel would then allow the F 1 hybrids to self-pollinate to produce an F 2 generation.
  • Wrinkled seeds in pea plants with two copies of the recessive allele are due to the accumulation of monosaccharides and excess water in seeds because of the lack of a key enzyme. The seeds wrinkle when they dry. Both homozygous dominants and heterozygotes produce enough enzyme to convert all the monosaccharides into starch and form smooth seeds when they dry.
  • 52 ch13mendel2007

    1. 1. Genetics & The Work of MendelAP Biology
    2. 2. Gregor Mendel  Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas  used experimental method  used quantitative analysis  collected data & counted them  excellent example of scientific methodAP Biology
    3. 3. Mendel’s work Pollen transferred from white flower to stigma of purple flower Bred pea plants P  cross-pollinate true breeding parents (P)  P = parental anthers removed  raised seed & then all purple flowers result observed traits (F1)  F = filial F1  allowed offspring to self-pollinate & observed next self-pollinate generation (F2) F2AP Biology
    4. 4. Mendel collected data for 7 pea traitsAP Biology
    5. 5. Looking closer at Mendel’s work true-breeding true-breeding X white-flower peasP purple-flower peas 100%F1 purple-flower peasgeneration 100%(hybrids) self-pollinate 75% 25% purple-flower peas white-flower peas 3:1F2generationAP Biology
    6. 6. What did Mendel’s findings mean?  Traits come in alternative versions  purple vs. white flower color  alleles  different alleles vary in the sequence of nucleotides at the specific locus of a gene  some difference in sequence of A, T, C, Gpurple-flower allele &white-flower allele are two DNAvariations at flower-color locusdifferent versions of gene atsame location on homologouschromosomesAP Biology
    7. 7. Traits are inherited as discrete units  For each characteristic, an organism inherits 2 alleles, 1 from each parent  diploid organism  inherits 2 sets of chromosomes, 1 from each parent  homologous chromosomes  like having 2 editions of encyclopedia  Encyclopedia Britannica  Encyclopedia Americana What are the advantages of being diploid?AP Biology
    8. 8. What did Mendel’s findings mean?  Some traits mask others  purple & white flower colors are I’ll speak for separate traits that do not blend both of us!  purple x white ≠ light purple  purple masked white  dominant allele allele producing mutant allele  functional protein functional protein malfunctioning  affects characteristic protein  masks other alleles homologous  recessive allele chromosomes  no noticeable effect  allele makes aAP Biology malfunctioning protein
    9. 9. Genotype vs. phenotype  Difference between how an organism “looks” & its genetics  phenotype  description of an organism’s trait  genotype  description of an organism’s genetic makeup P X Explain Mendel’s results using purple white …dominant & recessive …phenotype & genotype F1AP Biology all purple
    10. 10. Making crosses  Can represent alleles as letters  flower color alleles → P or p  true-breeding purple-flower peas → PP  true-breeding white-flower peas → pp P X PP x pp purple white F1 all purple PpAP Biology
    11. 11. Looking closer at Mendel’s work true-breeding true-breeding X white-flower peas phenotypeP purple-flower peas PP pp genotype 100%F1 purple-flower peasgeneration 100%(hybrids) Pp Pp Pp Pp self-pollinate 75% 25% purple-flower peas white-flower peas 3:1F2generationAP Biology ? ? ? ?
    12. 12. Aaaaah, phenotype & genotype Punnett squares can have differentF1 Pp x Pp ratiosgeneration(hybrids) % % genotype phenotype male / sperm PP 25% P p Pp 75% PP Pp 50% PpP pfemale / eggs Pp pp pp 25% 25%AP Biology 1:2:1 3:1
    13. 13. Genotypes  Homozygous = same alleles = PP, pp  Heterozygous = different alleles = Pp homozygous dominant heterozygous homozygous recessiveAP Biology
    14. 14. Phenotype vs. genotype  2 organisms can have the same phenotype but have different genotypes purple PP homozygous dominant purple Pp heterozygous Can’t tell by lookin’ at ya! How do you determine the genotype of an individual with with a dominant phenotype?AP Biology
    15. 15. Test cross  Breed the dominant phenotype — the unknown genotype — with a homozygous recessive (pp) to determine the identity of the unknown allele x How does that work? is it pp PP or Pp?AP Biology
    16. 16. How does a Test cross work? x x PP pp Pp pp p p p p P Pp Pp P Pp Pp P Pp Pp p pp ppAP Biology 100% purple 50% purple:50% white or 1:1
    17. 17. Mendel’s 1st law of heredity PP P  Law of segregation  during meiosis, alleles segregate P  homologous chromosomes separate  each allele for a trait is packaged into pp a separate gamete p p Pp PAP Biology p
    18. 18. Law of Segregation  Which stage of meiosis creates the law of segregation? Metaphase 1 Whoa! And Mendel didn’t even know DNA or genes existed!AP Biology
    19. 19. Monohybrid cross  Some of Mendel’s experiments followed the inheritance of single characters  flower color  seed color  monohybrid crossesAP Biology
    20. 20. Dihybrid cross  Other of Mendel’s experiments followed the inheritance of 2 different characters  seed color and seed shape  dihybrid crosses Mendel was working out many of the genetic rules!AP Biology
    21. 21. Dihybrid cross true-breeding true-breedingP yellow, round peas x green, wrinkled peas Y = yellow YYRR yyrr y = green R = round r = wrinkledF1 yellow, round peasgeneration 100%(hybrids) YyRr self-pollinate 9:3:3:1F2generation 9/16 3/16 3/16 1/16 yellow green yellow green round round wrinkled wrinkledAP Biology peas peas peas peas
    22. 22. What’s going on here?  If genes are on different chromosomes…  how do they assort in the gametes?  together or independently? YyRr Is it this? Or this? YyRr YR yr YR Yr yR yr Which system explains theAP Biology data?
    23. 23. YyRr YyRr or Is this the way it works? YR yr YR Yr yR yr YyRr x YyRr 9/16 yellow round YR yr 3/16 green round Well, that’s YR YYRR YyRr NOT right! 3/16 yellow wrinkled yr YyRr yyrr 1/16 green wrinkledAP Biology
    24. 24. YyRr YyRr or Dihybrid cross YR yr YR Yr yR yr YyRr x YyRr 9/16 yellow round YR Yr yR yr 3/16 YR YYRR YYRr YyRR YyRr green round Yr YYRr YYrr YyRr Yyrr BINGO! 3/16 yellow wrinkled yR YyRR YyRr yyRR yyRr 1/16 yr YyRr Yyrr yyRr yyrr green wrinkledAP Biology
    25. 25. Can you think of an exception Mendel’s 2nd law of heredity to this?  Law of independent assortment  different loci (genes) separate into gametes independently yellow  non-homologous chromosomes align independently green  classes of gametes produced in equal amounts  YR = Yr = yR = yr round  only true for genes on separate chromosomes or on same chromosome but so far apart that crossing wrinkled over happens frequently YyRrYr Yr yR yR YR YR yr yr 1AP Biology : 1 : 1 : 1
    26. 26. Law of Independent Assortment  Which stage of meiosis creates the law of independent assortment? Remember Metaphase 1 Mendel didn’teven know DNA —or genes— existed! EXCEPTION  If genes are on same chromosome & close together  will usually be inherited together  rarely crossover separatelyAP Biology  “linked”
    27. 27. The chromosomal basis of Mendel’s laws… Trace the genetic events through meiosis, gamete formation & fertilization to offspringAP Biology
    28. 28. Review: Mendel’s laws of heredity  Law of segregation  monohybrid cross  single trait  each allele segregates into separate gametes  established by Metaphase 1  Law of independent assortment  dihybrid (or more) cross  2 or more traits  genes on separate chromosomes assort into gametes independently  established by Metaphase 1 EXCEPTIONAP Biology  linked genes metaphase1
    29. 29. Mendel chose peas wisely  Pea plants are good for genetic research  available in many varieties with distinct heritable features with different variations  flower color, seed color, seed shape, etc.  Mendel had strict control over which plants mated with which  each pea plant has male & female structures  pea plants can self-fertilize  Mendel could also cross-pollinate plants: moving pollen from one plantAP Biology to another
    30. 30. Mendel chose peas luckily  Pea plants are good for genetic research  relatively simple genetically  most characters are controlled by a single gene with each gene having only 2 alleles,  one completely dominant over the otherAP Biology
    31. 31. Any Questions??AP Biology

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