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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 F1 generation.
    Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 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 F1 generation.
    Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 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.

Transcript

  • 1. Genetics & The Work of Mendel AP Biology 2006-2007
  • 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  AP Biology excellent example of scientific method
  • 3. Mendel’s work  Bred pea plants  Pollen transferred from white flower to stigma of purple flower P cross-pollinate true breeding parents (P)  P = parental  raised seed & then observed traits (F1)  F = filial  allowed offspring to self-pollinate & observed next generation (F2) AP Biology anthers removed all purple flowers result F1 self-pollinate F2
  • 4. Mendel collected data for 7 pea traits AP Biology
  • 5. Looking closer at Mendel’s work P F1 true-breeding true-breeding X white-flower peas purple-flower peas 100% purple-flower peas Where did the white flowers go? 100% generation (hybrids) self-pollinate F2 generation AP Biology 75% purple-flower peas White flowers came back! 25% white-flower peas 3:1
  • 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, G purple-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous chromosomes AP Biology
  • 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 AP Biology What are the advantages of being diploid?
  • 8. What did Mendel’s findings mean?  Some traits mask others  purple & white flower colors are separate traits that do not blend I’ll speak for both of us!  purple x white ≠ light purple  purple masked white  dominant allele  functional protein  masks other alleles  mutant allele producing malfunctioning protein recessive allele  allele makes a malfunctioning protein AP Biology wild type allele producing functional protein homologous chromosomes
  • 9. Genotype vs. phenotype  Difference between how an organism “looks” & its genetics  phenotype  description of an organism’s trait  the “physical”  genotype  description of an organism’s genetic makeup Explain Mendel’s results using …dominant & recessive …phenotype & genotype AP Biology X P purple white F1 all purple
  • 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  PP x pp X P purple white F1 AP Biology all purple Pp
  • 11. Looking closer at Mendel’s work P true-breeding true-breeding X white-flower peas phenotype purple-flower peas PP pp 100% purple-flower peas F1 genotype 100% generation (hybrids) Pp Pp Pp Pp self-pollinate F2 generation AP Biology 75% purple-flower peas ? ? ? 25% white-flower peas ? 3:1
  • 12. Punnett squares Pp x Pp F1 Aaaaah, phenotype & genotype can have different ratios generation (hybrids) % genotype male / sperm female / eggs P p PP Pp P PP Pp p Pp pp AP Biology % phenotype 25% 75% 50% Pp pp 25% 25% 1:2:1 3:1
  • 13. Genotypes  Homozygous = same alleles = PP, pp  Heterozygous = different alleles = Pp homozygous dominant heterozygous homozygous recessive AP Biology
  • 14. Phenotype vs. genotype  2 organisms can have the same phenotype but have different genotypes purple PP homozygous dominant purple Pp heterozygous How do you determine the genotype of an individual with with a dominant phenotype? AP Biology Can’t tell by lookin’ at ya!
  • 15. Test cross  Breed the dominant phenotype — the unknown genotype — with a homozygous recessive (pp) to determine the identity of the unknown allele How does that work? x is it PP or Pp? AP Biology pp
  • 16. How does a Test cross work? Am I this? Or am I this? x PP pp x Pp p p P Pp Pp P Pp Pp P Pp Pp p pp pp AP Biology 100% purple p pp p 50% purple:50% white or 1:1
  • 17. Mendel’s 1st law of heredity PP  Law of segregation  during meiosis, alleles segregate P P  homologous chromosomes separate  each allele for a trait is packaged into a separate gamete p pp p P Pp AP Biology p
  • 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. Monohybrid cross  Some of Mendel’s experiments followed the inheritance of single characters flower color  seed color  monohybrid crosses  AP Biology
  • 20. Dihybrid cross  Other of Mendel’s experiments followed the inheritance of 2 different characters seed color and seed shape  dihybrid crosses  AP Biology Mendel was working out many of the genetic rules!
  • 21. Dihybrid cross P true-breeding yellow, round peas Y = yellow R = round x YYRR yyrr true-breeding green, wrinkled peas y = green r = wrinkled yellow, round peas F1 generation (hybrids) 100% YyRr self-pollinate F2 generation AP Biology 9:3:3:1 9/16 yellow round peas 3/16 green round peas 3/16 yellow wrinkled peas 1/16 green wrinkled peas
  • 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? YR AP Biology yr Or this? YR YyRr Yr Which system explains the data? yR yr
  • 23. YyRr Is this the way it works? YR YyRr x YyRr or yr YyRr YR Yr yR yr 9/16 yellow round YR YR yr AP Biology yr YYRR YyRr YyRr yyrr Well, that’s NOT right! 3/16 green round 3/16 yellow wrinkled 1/16 green wrinkled
  • 24. YyRr Dihybrid cross YR YyRr x YyRr YR Yr yR yr or YR Yr yr YyRr Yyrr yR YyRR YyRr yyRR yyRr yr AP Biology YYRr YyRr YYrr Yyrr yyRr yyrr yR yr 9/16 yellow round 3/16 green round YR YYRR YYRr YyRR YyRr Yr YyRr BINGO! 3/16 yellow wrinkled 1/16 green wrinkled
  • 25. Mendel’s 2nd law of heredity Can you think of an exception to this?  Law of independent assortment  yellow different loci (genes) separate into gametes independently green  non-homologous chromosomes align independently  classes of gametes produced in equal amounts round  only true for genes on separate chromosomes or  YR = Yr = yR = yr wrinkled on same chromosome but so far apart that crossing over happens frequently YyRr Yr Yr 1 AP Biology yR : yR 1 YR : YR 1 yr : yr 1
  • 26. Law of Independent Assortment  Which stage of meiosis creates the law of independent assortment? Remember Mendel didn’t even know DNA —or genes— existed! AP Biology Metaphase 1 EXCEPTION  If genes are on same chromosome & close together  will usually be inherited together  rarely crossover separately  “linked”
  • 27. The chromosomal basis of Mendel’s laws… Trace the genetic events through meiosis, gamete formation & fertilization to offspring AP Biology
  • 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 AP Biology EXCEPTION  linked genes metaphase1
  • 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 AP Biology structures  pea plants can self-fertilize  Mendel could also cross-pollinate plants: moving pollen from one plant to another
  • 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 other AP Biology
  • 31. Any Questions?? AP Biology 2006-2007