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

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4. Mendelian Genetics Topics: - Transmission of DNA during cell division - Transmission of DNA during cell division Mitosis and Meiosis Mitosis and Meiosis - Segregation - Segregation - Sex linkage - Sex linkage - Inheritance and probability - Inheritance and probability - Independent Assortment - Independent Assortment - Mendelian genetics in humans - Mendelian genetics in humans - Linkage - Linkage - Gene mapping - 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): Mitosis (somatic tissue): identical cells identical cells Meiosis (germ tissue): Meiosis (germ tissue): gametes (variation) gametes (variation) Behaviour of chromosomes can explain the behaviour of genes (segregation and independent assortment)

6. Chromosome and DNA Replication 1.DNA replication results in chromosome replication chromosome replication 2. Nuclear and cell division

7. Meiosis 2n n 2n2n Mitosis

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

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

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

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

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

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

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

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

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

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

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

24. Cross Pollination

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

26. Genetical Analysis (pea shape) Parental round X wrinkled cross F 1 (filial) round self F 2 3/4 round 1/4 wrinkled (3:1)

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

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

29. Hypothesis P AA X aa P AA X aa A a gametes A a gametes F 1 Aa F 1 Aa Self Aa X Aa Self Aa X Aa F 2 F 2

30. F2F2F2F2 Self F 1 Aa X Aa Self F 1 Aa X Aa equal equal segregation segregation 1/2 A 1/2 a 1/2 A 1/2 a 1/2 A 1/4 AA 1/4 Aa 1/2 A 1/4 AA 1/4 Aa 1/2 a 1/4 Aa 1/4 aa 1/2 a 1/4 Aa 1/4 aa F 2 Genotypes 1/4 AA 2/4Aa 1/4 aa (1:2:1) F 2 Phenotypes 3/4 A- 1/4 aa (3:1)

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

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

33. Genetic Terminology Genes: hereditary elements Alleles: forms of a gene: A a Heterozygote: Aa Homozygotes: AA aa GenotypesPhenotypes Dominance AA, Aa same phenotype different genotypes different genotypes

34. Summary Experimental: 1. Two pure breeding lines 1. Two pure breeding lines 2. Cross --------> F 1 hybrid 2. Cross --------> F 1 hybrid 3. Self F 1 ------> F 2 3. Self F 1 ------> F 2

35. Summary Results: 1. F 1 one phenotype 1. F 1 one phenotype 2. F 2 3:1 ratio of 2 phenotypes 2. F 2 3:1 ratio of 2 phenotypes

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

37. observed Expected 3 : 1 DominantPhenotype AA x aa ------  Aa ----  ¾ AA, Aa ¼ aa P F 1 F 2 P F 1 F 2

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

39. Virtual Fly

40. F 1 Parents X

41. F 2 3 wildtype.. 1 vestigial

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

43. Principle of Segregation Implications 1.Answer questions on inheritance 2.Explore other questions

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

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

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

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

48. Sex Linkage reciprocal crosses X X Round wrinkled Round wrinkled X X wrinkled Round wrinkled Round

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

50. Red Eye White eye Drosophila

51. Cross A red female X white male F 1 all red F 1 all red F 2 red : white F 2 red : white 3 : 1 3 : 1 white all male white all male red 2 : 1 female : male red 2 : 1 female : male

52. Cross B white female X red male F 1 females males F 1 females males F 2 females males F 2 females males 1 : 1 : 1 : 1 1 : 1 : 1 : 1

53. Conclusions 1. Sex and eye-colour gene associated 2. Criss-cross inheritance 2. Criss-cross inheritance - daughters inherit father’s phenotype - daughters inherit father’s phenotype - sons inherit mother’s phenotype - sons inherit mother’s phenotype

54. Interpretation Sex chromosomes (X, Y) Females: 3 pairs of autosomes Females: 3 pairs of autosomes 1 pair of sex chromosomes (XX) 1 pair of sex chromosomes (XX) Males: 3 pairs of autosomes Males: 3 pairs of autosomes 1 heteromorphic pair (XY) 1 heteromorphic pair (XY)

55. Male Female autosomes Chromosomes

56. Explanation Eye colour gene on X chromosome Eye colour gene on X chromosome Wildtype (red) dominant to white Wildtype (red) dominant to white sex chromosomes eye-colour genotype sex chromosomes eye-colour genotype Females X X WW Ww ww Males X Y W w white Red

57. Alternative Notation eye-colour genotype eye-colour genotype Females w + w + w + w ww Males w + Y wY Eye colour

58. Cross A Cross B Cross A Cross BFEMALEMALE Fig. 5-8

59. Cross A Cross B Cross A Cross B F 1 F 2 X X

60. Cross B ww X w + Y ww X w + Y F 1 ww + wY F 1 ww + wY F 2 w Y F 2 w Y w ww wY w ww wY w + ww + w + Y w + ww + w + Y 1 : 1 : 1 : 1

61. Conclusion 1. Eye colour gene associated with sex chromosome (X) 2. Eye colour not related to sexual function. Genes on sex chromosomes not related to sexual function

62. Sex Determination XX XY XXY XO XX XY XXY XO Drosophila * Human * * * Sterile * Sterile klinefelter turner Homogametic Heterogametic

63. Sex Determination Humans: Y chr. -------> maleness Drosophila: sex -----> X/A ratio 2X/2A = 1.0 ------> 2X/2A = 1.0 ------> X/2A = 0.5 ------> X/2A = 0.5 ------>

64. Gynandromorphs X w,m X w,m X w,m X +,+ X w,m X +,+ Nondisjunction during Early development (mitotic cell division) Normal mitosis X w,m X +,+ X w,m X +,+ Wild female X w,m X +,+ X w,m X +,+ X w,m X w,m X w,m X +,+ X w,m X +,+

65. Gynandromorphs X w,m X w,m X w,m X +,+ X w,m X +,+ Nondisjunction during Early development

66. Other sex determining systems Birds & Moths Birds & Moths homogametic heterogametic homogametic heterogametic ZZ ZW ZZ ZW

67. Sex Linkage (X Y) - Y chromosome lacks homology - Y chromosome lacks homology with X with X - alleles on X expressed in males - alleles on X expressed in males - hemizygous : a gene present in - hemizygous : a gene present in one copy X w Y one copy X w Y

68. Summary Traits controlled by a single gene: - precise Mendelian ratios: 3:1, 1:1, 1:2:1 - precise Mendelian ratios: 3:1, 1:1, 1:2:1 - ratios due to chromosome segregation - ratios due to chromosome segregation during meiosis during meiosis - sex linked inheritance  sex chromosomes - sex linked inheritance  sex chromosomes