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March 15, 2012

March 15, 2012. BellRinger List 5 examples of instances where you have observed evidence of inherited traits between parents and offspring. Objectives Differentiate between the particulate and blended hypothesis of inheritance Use Punnett squares to predict phenotypic and genotypic outcomes

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March 15, 2012

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  1. March 15, 2012 • BellRinger • List 5 examples of instances where you have observed evidence of inherited traits between parents and offspring. • Objectives • Differentiate between the particulate and blended hypothesis of inheritance • Use Punnett squares to predict phenotypic and genotypic outcomes • Homework • Chp 14 (sec 3)

  2. Genetics • How are traits inherited? • Debate between two hypothesis: • Particulate hypothesis • traits from parents are joined, but remain discrete • Blended hypothesis • traits are mixed to become a third trait

  3. Blended hypothesis • P generation (true breeders) coffee and cream • What type of offspring can the parents make? • (mix the coffee & the cream=mocha colored) • F1 generation (mocha colored) • What type of offspring can the F1 generation make? • Pour out into 4 cups-only mocha colored F2 gen • Can the two traits for the characteristic of color be separated out? • Do we see examples of this type of character blending in real life?

  4. Yes!

  5. Particulate hypothesis • Two cups with different color marbles in each “true-breeders” • What type of offspring can the parents of this cross make? (mix the beads) • What types of offspring can the F1 generation make? • Make F2 gen by separating the colors out in two cups and mixing the colors in two cups • Can the two traits for the characteristic of color be separated out again? • Do we see examples of this type of character mixing in real life?

  6. Yes!

  7. Learning Check • Which hypothesis, particulate or blended, is more likely to explain inheritance of traits?

  8. 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 • usedquantitative analysis • collected data & counted them • excellent example of scientific method

  9. 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 plant to another

  10. 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 versions (alleles) • one completely dominant over the other

  11. Mendel’s work Pollen transferred from white flower to stigma of purple flower • Bred pea plants • 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) P anthers removed all purple flowers result F1 self-pollinate F2

  12. Mendel collected data for 7 pea traits

  13. true-breeding purple-flower peas true-breeding white-flower peas 100% purple-flower peas F1 generation (hybrids) 100% 75% purple-flower peas 25% white-flower peas 3:1 F2 generation Looking closer at Mendel’s work X P Where did the whiteflowers go? Whiteflowers cameback! self-pollinate

  14. What did Mendel’s findings mean? • 4 conclusions 1. 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

  15. Traits are inherited as discrete units 2. 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 theadvantages ofbeing diploid?

  16. What did Mendel’s findings mean? 3. Some traits mask others • purple & white flower colors are separate traits that do not blend • purple x white ≠ light purple • purplemaskedwhite • dominant allele • functional protein • masks other alleles • recessive allele • allele makes a malfunctioning protein I’ll speak for both of us! mutantallele producingmalfunctioningprotein wild typeallele producingfunctional protein homologouschromosomes

  17. P P P p PP Pp pp p p Mendel’s 1st law of heredity 4. Law of segregation • during meiosis, alleles segregate • homologous chromosomes separate • each allele for a trait is packaged into a separate gamete

  18. Metaphase 1 Law of Segregation • Which stage of meiosis creates the law of segregation? Whoa!And Mendeldidn’t even knowDNA or genesexisted!

  19. Learning Check • Summarize the 4 parts of Mendel’s model of inheritance

  20. X P purple white F1 all purple Some Vocabulary • 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

  21. Genotypes • Homozygous = same alleles = PP, pp • Heterozygous = different alleles = Pp homozygousdominant heterozygous homozygousrecessive

  22. purple PP homozygous dominant purple Pp heterozygous How do you determine the genotype of an individual withwith a dominant phenotype? Phenotype vs. genotype • 2 organisms can have the same phenotype but have different genotypes

  23. x 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? is itPP or Pp? pp

  24. x x How does a Test cross work? Am I this? Or am I this? PP pp Pp pp p p p p P P Pp Pp Pp Pp P p Pp Pp pp pp 100% purple 50% purple:50% whiteor 1:1

  25. Monohybrid cross • Some of Mendel’s experiments followed the inheritance of single characters • flower color • seed color • monohybrid crosses

  26. PP pp x X P purple white F1 all purple 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

  27. true-breeding purple-flower peas true-breeding white-flower peas 100% purple-flower peas F1 generation (hybrids) 100% 75% purple-flower peas 25% white-flower peas Looking closer at Mendel’s work phenotype X P PP pp genotype Pp Pp Pp Pp self-pollinate 3:1 F2 generation ? ? ? ?

  28. PP 25% male / sperm P p Pp 50% 75% P Pp female / eggs pp p 25% 25% Aaaaah, phenotype & genotypecan have different ratios Punnett squares Pp x Pp F1 generation (hybrids) % genotype % phenotype PP Pp Pp pp 1:2:1 3:1

  29. March 16, 2012 • BellRinger: • Consider two peas with the following genotypes: IIGG x iigg I=inflated pod G=green pod i=constricted pod g=yellow pod • How many traits or genes are represented by these genotypes? • When gametes are made in meiosis, how many alleles does each gamete get of a single gene? • Objectives • Predict the genotype and phenotype probabilities of two genes • Homework • Chp 15 (sec 1-3)

  30. Dihybrid Crosses • What types of gametes can the dominant parent make? • What types of gametes can the recessive parent make? • What type(s) of offspring will be produced by a cross between these two parents? • If the F1 generation of the plants was allowed to cross, what types of gametes would result?

  31. Dihybrid cross • Other of Mendel’s experiments followed the inheritance of 2 different characters • seed color andseed shape • dihybrid crosses

  32. F1 generation (hybrids) yellow, round peas 100% F2 generation Dihybrid cross P true-breeding yellow, round peas true-breeding green, wrinkled peas x YYRR yyrr Y = yellow R = round y = green r = wrinkled YyRr self-pollinate 9:3:3:1 9/16 yellow round peas 3/16 green round peas 3/16 yellow wrinkled peas 1/16 green wrinkled peas

  33. YR YR yR Yr yr yr YyRr What’s going on here? • If genes are on different chromosomes… • how do they assort in the gametes? • together or independently? Is it this? Or this? YyRr Which systemexplains the data?

  34. 9/16 yellow round YyRr YyRr 3/16 green round YR yr YR yR Yr yr 3/16 yellow wrinkled 1/16 green wrinkled or Is this the way it works? YyRr x YyRr YR yr  Well, that’sNOT right! YR YYRR YyRr yr YyRr yyrr

  35. 9/16 yellow round YyRr YyRr 3/16 green round YR YR yr YR yR Yr yr Yr 3/16 yellow wrinkled yR 1/16 green wrinkled yr or Dihybrid cross YyRr x YyRr YR Yr yR yr  YYRR YYRr YyRR YyRr BINGO! YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr

  36. yellow green round wrinkled Can you thinkof an exceptionto this? Mendel’s 2nd law of heredity • Law of independent assortment • different loci (genes) separate into gametes independently • non-homologous chromosomes align independently • classes of gametes produced in equal amounts • YR = Yr = yR = yr • only true for genes on separate chromosomes or on same chromosome but so far apart that crossing over happens frequently YyRr Yr Yr yR yR YR YR yr yr 1 : 1 : 1 : 1

  37. Metaphase 1 Law of Independent Assortment • Which stage of meiosis creates the law of independent assortment? RememberMendel didn’teven know DNA—or genes—existed! EXCEPTION • If genes are on same chromosome & close together • will usually be inherited together • rarely crossover separately • “linked”

  38. 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 EXCEPTION • linked genes metaphase1

  39. Dihybrid crosses-summary • Do both dominant alleles have to go to the same gamete? • Can a gamete have a mixture of dominant and recessive alleles? (Do you have a mixture of dominant and recessive traits from your parents?) • How is each gene segregated independently when they are all on a limited number of chromosomes? • Complete dihybrid practice problems

  40. Any Questions??

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