Essential Biology 10.2 Dihybrid Crosses & Gene Linkage (AHL)


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Essential Biology 10.2 Dihybrid Crosses & Gene Linkage (AHL)

  1. 1. Blog resource: Click4Biology: <br />Cite all sources using the CSE method (or ISO 690 Numerical in Word. Highlight all objective 1 command terms in yellow and complete these before class. Highlight all objective 2 and 3 command terms in green – these will be part of the discussions in class. After class, go back and review them. <br />Complete the self-assessment rubric before submitting to Moodle. Avoid printing this if possible. <br /><ul><li>Distinguish between dihybrid and monohybrid crosses.
  2. 2. Mono-
  3. 3. Di-
  4. 4. When Mendel came upon his law of independent assortment, he was studying sweet-pea colour and shape. These traits are carried on separate chromosomes. The colour yellow (Y) is dominant over green (y). Smooth peas (S) are dominant over rough (s).
  5. 5. State the law of independent assortment.
  6. 6.
  7. 7. State the possible genotypes for the following phenotypes:
  8. 8. Yellow, SmoothGreen, SmoothGreen, roughyyss onlyYellow, rough
  9. 9. 24765039370000Use the punnet grid to predict the ratio of phenotypes of offspring in a cross between two peas which are heterozygous for both genes (SsYy x SsYy).
  10. 10. SYSysYsySYSysYsy</li></ul>PhenotypeSmooth Yellow Smooth green Rough Yellow Rough GreenRatio<br /><ul><li>A researcher has some smooth yellow peas. He wants to find out if they are homozygous or heterozygous for these dominant characteristics, so he performs a test cross.
  11. 11. State the genotype and phenotype of the plant that must be used as the test cross.
  12. 12. Genotype:
  13. 13. Phenotype:
  14. 14. Complete a series of punnet grids for this cross.
  15. 15. Deduce the phenotype ratios expected in the following crosses.
  16. 16. Heterozygous for both colour and shape?</li></ul>PhenotypeRatio<br /><ul><li>Homozygous for both colour and shape.</li></ul>PhenotypeRatio<br /><ul><li>Heterozygous for colour, homozygous for shape.</li></ul>PhenotypeRatio<br /><ul><li>Homozygous for colour, heterozygous for shape.
  17. 17. CACA</li></ul>PhenotypeRatio<br /><ul><li>In the cross, the student found 120 yellow-smooth and 124 green-smooth. Deduce the most likely genotype for the unknown pea. Explain your answer.
  18. 18. Genotype:
  19. 19. Explanation:
  20. 20. State the statistical test used to test for significance of difference between observed and expected outcomes.
  21. 21. Some genes affect the expression of others.
  22. 22. Define gene interaction.
  23. 23. Identify the phenotype ratios for a cross between two ‘agouti’ (brown) mice, where:
  24. 24. Gene C determines if colour is present: C = coat has colour c = albino
  25. 25.
  26. 26. If colour is present, then:A = agouti (brown)a = black
  27. 27. The mice are both heterozygous for both genes.
  28. 28. CACA</li></ul>PhenotypeRatio<br /><ul><li>Explain why the phenotype ratio is not 9:3:3:1.
  29. 29.
  30. 30.
  31. 31. Mendel’s law of independent assortment makes the assumption that genes for a pair or group of traits are being carried on separate chromosomes, and therefore the presence of one allele in a gamete is not connected to the presence of another.
  32. 32. However, with hundreds of genes per chromosome, it is likely that some genes will be physically linked and therefore alleles will be inherited together.
  33. 33. Define linkage groups.
  34. 34. State the consequence of gene linkage in terms of the movement of alleles in anaphase I.
  35. 35. Linkage groups will not…
  36. 36. State two plant examples of gene linkage.
  37. 37.
  38. 38.
  39. 39. The notation shows genes of Zea mays (corn). It is described as “heterozygous at both loci”.
  40. 40. 47720253746500These are both traits related to the corn kernels.
  41. 41. Key: C = colour, c = no colour; W = waxy, w = no wax.
  42. 42. Draw some other possible combinations of these linked genes:
  43. 43. Homozygous dominant at both lociHomozygous recessive at locus 1. (you decide) – describe it
  44. 44. Complete a punnet grid to show the possible phenotypes produced by a cross between the corn that is heterozygous at both loci. Use correct notations and show your working. </li></ul>PhenotypeRatio<br /><ul><li>List the combinations of alleles which are not possible in the cross above (unless recombination takes place at Prophase I).
  45. 45.
  46. 46.
  47. 47. A small number of kernels which are coloured but not waxy appear in the offspring.
  48. 48. Explain the process that must have occurred for this to be the case.
  49. 49. Process:
  50. 50.
  51. 51.
  52. 52.
  53. 53.
  54. 54. State the stage of meiosis during which crossing over and exchange of alleles can occur.
  55. 55. 2667001936750Complete the punnet grid below:
  56. 56. P Lp lp lPpLlp lno recombinationwith crossing over (recombinants)
  57. 57. The term linkage is used in various ways in genetics.
  58. 58. Distinguish between autosomes and sex chromomes.
  59. 59.
  60. 60.
  61. 61. Distinguish between gene linkage and sex linkage.
  62. 62.
  63. 63. </li></ul>Complete further practice of dihybrid crosses and gene linkage using the faces that you made in the Genotype to Phenotype activity and on the Practice Problems sheet. Be sure to set out all answers clearly. <br />Works Cited BIBLIOGRAPHY 1. Allott, Andrew. IB Study Guide: Biology for the IB Diploma. s.l. : Oxford University Press, 2007. 978-0-19-915143-1.2. Mindorff, D and Allott, A. Biology Course Companion. Oxford : Oxford University Press, 2007. 978-099151240.3. Clegg, CJ. Biology for the IB Diploma. London : Hodder Murray, 2007. 978-0340926529.4. Campbell N., Reece J., Taylor M., Simon. E. Biology Concepts and Connections. San Fransisco : Pearson Benjamin Cummings, 2006. 0-8053-7160-5.5. Taylor, Stephen. Science Video Resources. [Online] Wordpress, 2010. Burrell, John. Click4Biology. [Online] 2010. IBO. Biology Subject Guide. [Online] 2007.<br />Self Assessment:<br />Essential BiologyAssessmentCriterionComplete (2)Partially complete (1)SelfMrTPresentation & OrganisationNAComplete and neat. All command terms highlighted, tables and diagrams well presented. Academic HonestyNASources cited using the CSE (ISO 690 numerical) method, with Works Cited section complete and correct. Objective 1 understandingAll answers for the following command terms correct:Most answers for the following command terms correct:Define Draw Label List Measure StateObjective 2 understandingAll answers for the following command terms correct:Most answers for the following command terms correct:Annotate Apply Calculate Describe Distinguish Estimate Identify OutlineObjective3understandingAll answers for the following command terms correct:Most answers for the following command terms correct:Analyse Comment Compare Construct Deduce Derive Design Determine DiscussEvaluate Explain Predict Show Solve Sketch SuggestLogic, notation, mathematical workingNAAnswers are presented in a logical and concise manner. SI units used most times, with correct unit symbols and definitions of terms. All mathematical working shown.Further researchNAEvidence is apparent of research and reading beyond the textbook and presentations to find correct answers to challenging questions. If any questions are unanswered, this criterion scores zero. Total (max 10):<br />