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Week 12

Week 12. Genetics I Chapter 11 pages 189-201 Genetics II Chapter 11 pages 202-209. EXAM III RESULTS. Total Students = 39 Total Pass= 15 (38.5%) Total Fail= 24 (61.5%) Class Average = 63 Top Score = 94 Low Score = 32. 8. 8. 7. 6. 5. 3. 2. A. B. C. D. F. F. F.

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Week 12

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  1. Week 12 Genetics I Chapter 11 pages 189-201 Genetics II Chapter 11 pages 202-209

  2. EXAM III RESULTS Total Students = 39 Total Pass= 15 (38.5%) Total Fail= 24 (61.5%) Class Average = 63 Top Score = 94 Low Score = 32

  3. 8 8 7 6 5 3 2 A B C D F F F

  4. TROUBLE SPOTS Questions answered incorrectly: #2 (61.5% (24/39)) #3(41% (16/39)) #9(46% (18/39)) #19 (67% (26/39)) #26 (47% (23/39)) #49 (69% (27/39)) #s 10 and 50 were well answered in general

  5. B. Pairing of homologous chromosomes only occurs in meiosis crossing over #49 A. MEIOSIS Pairing of x-somes

  6. HOMEWORK Chapter 12 ALL including Self-tests EXAM III Extra Credit- DUE MAY 10th

  7. Aneuploidy Euploidy= Correct number of chromosomes in a species Aneuploidy= A change in the number of chromosomes due to nondisjuction

  8. CHANGES IN CHROMOSOME STRUCTURE Changes in chromosome structures are mutations X-somes can break due to radiation, organic chemicals and viruses End of chromosomes break and can go back together improperly which leads to chromosomal mutations: Deletions Duplications Translocations Inversions

  9. Deletions Duplications Translocations Inversions

  10. DNA exists as chromatin or as a chromosome DNA- Deoxyribonucleic Acid A POLYMER of NUCLEOTIDES

  11. How do we know that certain complications will arise if genes are added or deleted to portions of chromosomes? Through the Study of Genetics! Genetics is the study of biologically inherited traits Ex. How will the deletion of section ‘a’ affect disease? Genomics is the study of all of the genes in an organism

  12. Genetics and Genomics ‘Inherited traits are determined by the elements of heredity that are transmitted from parent to offspring in reproduction; these elements of heredity are called genes.’ DNA is the molecule of heredity

  13. Gregor Mendel, 1822-1884 Austrian Monk Developed ‘Particulate Theory of Inheretance’ By studying Pea Plants in the 1860s Combined Math and Biology! Used statistics and laws of probability to study biology The Father of Genetics Darwin 1809-1882

  14. Mendel studied garden pea plants to understand the units of heredity WHY? At the time, the ‘Blending Concept of Inheritance’ was widely accepted Blending Concept of Inheritance= an offspring’s genetic makeup is intermediate to that of its parents Ex. A cross between red and white flowers will only generate PINK flowers Is this true?

  15. NO!! Because… Red, Pink and White flowers result in the 2nd Generation! Diverse forms could not evolve if the blending theory was correct.

  16. If we only had intermediate forms with little variation, how could all of the diversity we see have evolved? • Confused both Mendel and Darwin • Genes had not been discovered and would not be discovered until 1869 by • Friedrich Miescher • The molecular makeup of genes was discovered, but the function of genes was • still not well understood. • By 1900 it was understood that chromosome number is nearly constant in the cellsof any species. • Seemed likely that chromosomes were carriers of genes.

  17. How did Mendel and others come to the conclusion that chromosomes were thecarriers of genes? Through the study of phenotypes and crossings of pea plants with various traits PHENOTYPE The set of an organism’s observable properties resulting from the interaction of the organisms genotype with its environment GENOTYPE The genes present in a particular organism or cell ‘ATCCGCATTACG’

  18. Mendel’s 7 Pea Plant Traits P = Parental Generation F1= First Generation F2= Second Generation 1. 2. 3. 4. Garden Pea Plant Pisumsativum 5. 6. 7.

  19. Mendel’s Particulate Theory of Inheritance • Mendel used the scientific method to understand inheritance in pea plants • He created ‘pure’ or ‘true-breeding’ lines of plants for specific traits (ex. Round or smooth seeds, purple or white flowers…) • He observed and tracked these phenotypes through multiple generations of pea plants • Based on his studies, he determined that hereditary information is passed from parents to offspring in the form of discrete “particles” (which we now refer to as GENES)

  20. Why study the Garden Pea Plant? • Easy to cultivate • Short generation time • Can self pollinate - Able to create ‘true-breeders’ • Can cross pollinate by hand • Traits easy to observe • Can observe dominant or recessive characteristics

  21. ‘True-Breeding’ - Anther contain Sperm - Ovules in ovary contain Eggs - Pea plants are able to ‘self- pollinate’ - Therefore, offspring are identical to the parents - Mendel bred plants ‘true’ to ensure the purity of each trait

  22. Why secure the purity of each trait? • Had to ensure that the trait he was observing was not confounded by other discrete particles • Ex. He had to make sure that a white colored flower was truly white before making any crosses • His experiments would have failed because he would have observed different outcomes each generation

  23. Cross-Pollination After self pollinating plants for several generations to obtain ‘true-breeding’ plants Mendel used the anther from one true- bred plant to pollinate the Stigma of another true-bred plant= Cross Pollination From plant A onto the stigma of plant B

  24. Mendel’s Hypothesis Hypothesis Hereditary information is passed from parents to offspring in the form of discrete “particles”

  25. Mendel’s Observations (3:1, D:R)

  26. Mendel’s Laws Based on his observations of cross-pollination studies: • LAW OF SEGREGATION 2 LAW OF INDEPENDENT ASSORTMENT

  27. LAW OF SEGREGATION Based on the hypothesis that if the blending theory of inheritance were true, then a cross should yield an “intermediate” phenotype in comparison to the parents Ex. Tall plant x Short plant = Medium plant Mendel tested this by crossing plant varieties that differed by only 1 single trait…

  28. LAW OF SEGREGATION Mendel performed ‘reciprocal’ crosses: Dusted pollen of Tall plants onto Short plants Dusted pollen of short plants onto Tall plants All F1 resembled the TALL parent! NOT intermediate! Mendel allowed the F1s to self-pollinate  ¾ of the F2 plants were Tall and ¼ of the F2 plants were short!

  29. ALL F1s were Tall No intermediates observed! ALL F1s would have had the same genetic makeup because the parents were bred true.

  30. ALL of the F1 generation plants would have had a Tt genotype One T from parent 1 (bred true for TALL) and one t from parent 2 (bred true for SHORT) What happens when you cross two F1 generation plants? X

  31. Gametes A true-bred TALL plant gametes will only be T A true-bred SHORT plant gametes will only be t

  32. Gametes THEREFORE, the ONLY resulting GENOTYPE for the F1 generation is T t

  33. F1 CROSS The F1s are all Tt, therefore when Cross with each other It is a ‘mono’(one type) ‘hybrid’ (Tt) cross What will the GENOTYPES of the GAMETES look like for this MONOHYBRID CROSS? X

  34. What will the GENOTYPES of the GAMETES look like for this F1 MONOHYBRIDCROSS? F1 F1 T t T t T T t t


  36. 3:1 TALL: SHORT Dominant:Recessive Monohybrid crosses ALWAYS result in a 3:1 ratio The SHORT trait is masked by the TALL trait in the F1 generation and is observed in the F2 generation TALL is a dominant trait and SHORT is a recessive trait

  37. LAW OF SEGREGATION • Each individual has two factors for each trait • The factors ‘segregate’ during the formation of gametes • Each gamete contains only one factor from each pair of factors • Fertilization gives each new individual two factors for each trait (haploiddiploid) PAGE 192

  38. Dominance ‘Tallness’ in pea plants is dominant to ‘shortness’ Tall = T Short= t If parent 1 = TT (tall plant)and parent 2 = tt (short plant) ALL F1 generation plants will be Tt

  39. Dominance Genes occur at a particular ‘locus’ on a chromosome Alternative versions of the same gene are called ‘alleles’ The dominant allele masks the expression of the recessive allele

  40. Alleles= Alternative versions of the same gene A gene occurs at a particular locus MOM DAD If purple is dominant to white, the purple phenotype is observed, but you are a carrier for white! Remember: only 1 allele of each trait is in a gamete (meiosis!)

  41. GENOTYPES TT = Homozygous dominant (Tall Plant) Tt = Heterozygous (Tall Plant) tt = Homozygous recessive (Short Plant) Phenotypes

  42. PUNNETT SQUARES • Used to predict breeding outcomes • Able to calculate probability of traits Example: T t T t tt tt

  43. MENDEL’S LAW OF INDEPENDENT ASSORTMENT Mendel experimented with plants that differed in 2 traits The plants are hybrid in 2 ways therefore the crosses between the F1 generation are ‘DIHYBRID CROSSES’

  44. 2 traits Tall Green pods 2 traits short Yellow pods

  45. DiHybrid Cross Cont.’d X ? ? F1 GAMETES Sperm Eggs

  46. DiHybrid Cross Cont.’d X TG Tg tG tg TG Tg tG tg F1 GAMETES Sperm Eggs

  47. Mendel’s Dihybrid Cross Hypothesis I If the dominant factors always segregate together (=TG) and the recessive factors segregate together (=tg), then there would be two phenotypes among the F2 plants ONLY, tall plants (T) with green pods(G) and short plants (t) with yellow pods (g) Did Mendel observe this to be true? NO!!!

  48. Mendel’s Dihybrid Cross Hypothesis II If the four factors (T, G, t, g) segregate into the F1 gametes independently, then there would be four phenotypes among the F2 plants Tall and green pods Tall and yellow pods Short and green pods Short and yellow pods Did Mendel observe this to be true? YES!!!!!

  49. Mendel’s Dihybrid Cross Observations 9:3:3:1 9:3:3:1 Dihybrid crosses always have this phenotypic ratio!!!

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