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Biology 2250 Principles of Genetics

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  1. Biology 2250Principles of Genetics Announcements Test I marks are posted outside SN-3021 and in the lab. Exams will be returned Tuesday Spring Biology Courses at Harlow: http://www.mun.ca/harlow/

  2. Weekly Online Quizzes Marks Oct. 14 Example Quiz 2** for logging in Oct. 21 Quiz 1 2 Oct. 28 Quiz 2 2 Nov. 4 Quiz 3 2 Nov. 10 Quiz 4 2

  3. WebCT Quizzes Log in: http://webct.mun.ca:8900/

  4. Mendelian Genetics Topics: - Transmission of DNA during cell division Mitosis and Meiosis - Segregation - Sex linkage - Inheritance and probability - Independent Assortment - Mendelian genetics in humans - Linkage - Gene mapping - Tetrad Analysis (mapping in fungi) - Extensions to Mendelian Genetics - Gene mutation - Chromosome mutation - Quantitative and population genetics

  5. Basic Concepts of Genetics Cell/nuclear division Mitosis (somatic tissue): identical cells Meiosis (germ tissue): gametes (variation) Behaviour of chromosomes can explain the behaviour of genes (segregation and independent assortment)

  6. Chromosome and DNA Replication DNA replication results in chromosome replication 2. Nuclear and cell division

  7. Mitosis 2n 2n Meiosis 2n n

  8. Mitosis 1. one parent cell--------> 2 identical daughter cells 2. same in all organisms 3. simple: (a) each chromosome doubles (identical) (b) identical halves separate

  9. Meiosis(overview) diploid (2N) ---------------> haploid (N) gametes Chromosome replication once --------> 2 nuclear divisions (meiosis I, II) one nucleus -------------------> 4 nuclei

  10. Mitosis

  11. Meiosis I (reductional division) Pairing of homologous chromosomes Continued 

  12. Meiosis II (equational division) 4 products MEIOSIS ANIMATION (Textbook website)

  13. Comparison (Fig. 4-24) Mitosis Meiosis somatic cells cells of sexual cycle one doubling one doubling 1 division  2 cells 2 divisions  4 cells same amount of DNA ½ amount of DNA

  14. Comparison (continued) Mitosis Meiosis # chrs doesn’t change #chrs. halved No pairing of chr. Synapsis of homologs Centromeres divide at Not at anaphase I, anaphase but at anaphase II Conservative Variation

  15. Genetic Terminology Genes: hereditary elements Alleles: forms of a gene: A , a b, b+ Genotypes Gene pairs Heterozygote: Aa bb+ Homozygotes: AA aa bb b+ b+

  16. Genes on Chromosomes Expect behaviour of genes to correlate with the behaviour of chromosomes: genes chromosomes Diploid (2n) AA, Aa, aa pairs Haploid (n) A one set

  17. Genes Meiosis I A Correlation of genes and Chromosomes during meiosis a A Meiosis II b A B A A 1/2 A A OR a a a a b B 1/2 a a

  18. Mendelian Genetics Genes - cannot be observed directly Phenotypes - observed directly ** inheritance of phenotypes used to infer the inheritance of genes

  19. Mendelian Genetics Requirements: 1. Attributes of the phenotype that vary among individuals 2. Phenotypic variation caused by genetic differences

  20. Mendel’s Experiments Seven Pea varieties “True Breeding Lines” Character Phenotypes 1. seed shape round, wrinkled 2. seed colour yellow, green 3. flowers (pods) axial, terminal 4. pods full, constricted 5. pods yellow, green 6. flowers violet, white 7. stem tall, dwarf

  21. Advantages: easy to grow matures in a season self-fertilizing easy to cross fertilize

  22. Cross Pollination

  23. Mendel’s Experimental Approach suitable experimental organism examine few traits in each experiment accurate quantitative records analyzed data------> formulated hypotheses

  24. Genetical Analysis (pea shape) Parental round X wrinkled cross F1(filial) round self F2 3/4 round 1/4 wrinkled (3:1)

  25. Hypothesis to explain results 1. Hereditary determinants (genes) 2. Each adult plant has a gene pair (alleles) F1 plants: one allele dominant phenotype one allele recessive phenotype

  26. Hypothesis (continued) 3. Alleles of a gene pair segregate equally into the gametes 4. Each gamete has only one allele of a gene pair 5. Gametes combine at random to form zygote

  27. Hypothesis P AA X aa A a gametes F1Aa Self Aa X Aa F2

  28. F2 Self F1Aa X Aa equal segregation 1/2 A 1/2 a 1/2 A 1/4 AA 1/4 Aa 1/2 a 1/4 Aa 1/4 aa F2 Genotypes 1/4 AA 2/4Aa 1/4 aa (1:2:1) F2 Phenotypes 3/4 A- 1/4 aa (3:1)

  29. Test of Equal Segregation Hypothesis (Test Cross) round wrinkled R r X r r r 1/2 R 1/2 R r round 1/2 r 1/2 r r wrinkled 1:1 round:wrinkled

  30. Mendel’s First Law Equal segregation of two alleles of a gene pair during gamete formation

  31. Genetic Terminology Genes: hereditary elements Alleles: forms of a gene: A a Heterozygote:Aa Homozygotes:AA aa Genotypes Phenotypes DominanceAA, Aa same phenotype different genotypes

  32. Summary Experimental: 1. Two pure breeding lines 2. Cross --------> F1 hybrid 3. Self F1 ------> F2

  33. Summary Results: 1. F1 one phenotype 2. F2 3:1 ratio of 2 phenotypes

  34. Summary Inference: 1. Single major gene 2. dominant phenotype 3. equal segregation 4. existence of genes inferred

  35. P F1 F2 AA x aa ------ Aa ---- ¾ AA, Aa ¼ aa observed Expected 3 : 1 Dominant Phenotype

  36. Fig. 5-2 Bb Mendelian genetics applies to all organisms Correlation of genes and chromosomes Bb

  37. Virtual Fly

  38. Parents F 1 X

  39. F 2 3 wildtype .. 1 vestigial

  40. Parental AA x aa F1 Hybrid Aa Aa x Aa F2 AA Aa aa 1 : 2 : 1 (¼ ½ ¼ ) A a A AA Aa a Aa aa F2 ratio 3 : 1

  41. Principle of SegregationImplications Answer questions on inheritance Explore other questions

  42. Examples: 1. Parent Offspring Shell Colour Variation in the molluscs: Scallop: Hermaphodites self-fertilization dark orange dark 11 0 orange 12 45

  43. Examples 2. Paternity Families mother offspring father ? AA all AB BB AA 26AA, 24 AB AB AA 48 AA, 2 AB AA + BB ?

  44. Examples: 3. Detecting Hybrids: Species 1 Species 2 AA x BB Hybrids AB Mytilus Hybrid tross. edulis AB AA BB BB

  45. Sex-linked Inheritance Correlation between inheritance of genes and sex

  46. Sex Linkage reciprocal crosses X Roundwrinkled X wrinkled Round

  47. Drosophila melanogaster(T. H. Morgan) White eye (mutant) Red eye (wild) X

  48. Drosophila Red Eye White eye