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Introduction to DNA: Structure, Function, and Inheritance

Learn about DNA, its structure, the role it plays in cell activities, and how it is passed on from parents to offspring. Explore the concepts of genes, alleles, dominance, segregation, and independent assortment. Understand the complexities of genetic traits, disorders, and genetic diversity.

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Introduction to DNA: Structure, Function, and Inheritance

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  1. Lecture 009 DNA

  2. Gregor Mendel

  3. Rosalind Franklin Frances Crick & James Watson Proposed double helix model 1953 X-ray diffraction photograph of DNA, 1953

  4. Cell

  5. Nucleus

  6. DNA

  7. What is DNA? • DNA, or deoxyribonucleic acid, is the genetic instruction set. • It is composed of a linear sequence of units called nucleotides. • There are four different kinds of nucleotides (designated by the letters A, G, C, & T; sometimes called “bases”). • An individual DNA strand (or chromosome) may consist of 100,000’s of nucleotides. • The sequence of the nucleotides of a DNA strand determines the genetic code.

  8. DNA Polymers made up of individual nucleotides Nucleotides contain • Phosphate group • Five carbon sugar • Ring shaped nitrogen base DNA contains information for almost all cell activities

  9. Nucleotide Structure Nitrogen Base

  10. Nucleotide Bases Purines adenine guanine

  11. Nucleotide Bases Pyrimidines thymine cytosine

  12. Nucleotide Sugar Deoxyribose

  13. Polynucleotides =Nucleic Acids

  14. DNA is Double Stranded

  15. Base Pairing in DNA

  16. Double-Stranded DNA

  17. Chromosomes

  18. Chromosomes Come in Pairs

  19. Beliefs about Heredity • Fig. 1. De la propagation du genre humain, ou manuel indispensable pour ceux qui veulent avoir de beaux enfants de l’un ou l’autre sexe (Paris, Year VII). Image courtesy of the Bibliothèque Interuniversitaire de Médecine, Paris.

  20. Homunculus How is “heredity passed on: Spermist vs Ovists Spermist conception of a human sperm

  21. Homunculus Leeuwenhoek’s black male and white female rabbit experiments: spermist “proof”

  22. Darwin What he got right. What he got wrong. • Likes produce likes • Change can be permanent • There is no limit to cumulative change • Acquired characteristics Ex. Blind cave animals • Sex. Repro.- gemmules from all over body are packed in sperm and egg • Blended inheritance

  23. Mendel’s Three Principles • Dominance • Segregation • Independent Assortment (1822-1884) The foundation of “classical” science

  24. Genetic Definitions • Genes- genetic material on a chromosome that codes for a specific trait • Genotype- the genetic makeup of the organism • Phenotype- the expressed trait • Allel- an alternative form of a gene

  25. Dominance Mechanism • Two alleles are carried for each trait • In true-breeding individuals, both alleles are the same (homozygous). • Hybrids, on the other hand, have one of each kind of allele (heterozygous). • One trait is dominant, the other trait is recessive

  26. Dominance • Traits of both parents inherited, but one shows over the other • Traits are not blended

  27. Segregation • Half the gametes (egg or sperm) will carry the traits of one parent and half the traits for the other parent Pairs of alleles are separated (=segregated) during meiosis

  28. Independent Assortment Two different parental characteristics will be inherited independently of one another during gamete formation. Example: flower color and leaf shape

  29. Complexities • Multiple genes for one trait • Example: eye color • Blended traits (“incomplete dominance”) • Influence of the environment (UV, smoking, alcoholism)

  30. Complexities • Co-dominance-neither allele is recessive and the phenotypes of both alleles are expressed. • Blood types- AB (not O); sickle cell anemia heterochromia

  31. Disorders Down’s Syndrome (chrom 21) Alzheimer’s (chrom 1, 10, 14, 19, 21) Huntington’s (chrom 4)

  32. Genetic Information • Genes are traits • “Eye color” • Ear lobe connectedness • Genes produce proteins • Enzymes are proteins

  33. Homologous Chromosomes gene: location allele: specific trait

  34. Allele Example • Gene = “eye color” • Alleles • brown • blue • green • lavender

  35. Allele Examples appearance eye color:homozygous

  36. Allele Examples appearance eye color:heterozygous, brown dominant over blue

  37. Genotype vs Phenotype genotype phenotype homozygous(dominant) heterozygous homozygous (recessive) appearance Phaner = visible

  38. Punnett Square If male & female are heterozygous for eye color male female X brown: 3/4 offspring blue: 1/4 offspring

  39. Sickle Cell Anemia Each parent carries one gene for sickle cell S s S S S S s S s X S s S s s s s Possible genotypes: 1SS 2Ss 1ss Possible phenotypes:no sickle cell sickle cell

  40. Autosomes and Sex Chromosomes

  41. Red-Green Color Blindness Sex-linked trait XC Y XC Y XC XC XC Normal male XC Y X XC Xc XC Xc Xc Xc Y Normal female recessive gene Possible outcomes: XCXC XCXc XCY XcY Normal female Normal Female (carrier) Normal male Color-blind male

  42. allele gene E unconnected earlobe e connected earlobe unconnected P EE x ee E e gametes connected F1 Ee

  43. F1 Ee x Ee 1/2 E 1/2 e1/2 E 1/2 e gametes E e E EE Ee PunnettSquare e Ee ee F2 1 EE 2 Ee 1 ee

  44. Genotypes Phenotypes Experiment to determinedominant vs. recessive

  45. Genetic Sleuthing My eye color phenotype is brown. What is my genotype?

  46. Where Does Genetic Diversity Come From? • Mutation • Chromosomal Aberrations • Genetic Recombination (e.g., from sexual reproduction)

  47. Sickle Cell Mutation NORMAL Hb CTG ACT CCT GAG GAG AAG TCT Leu Thr Pro Glu Glu Lys Ser SICKLE CELL CTG ACT CCT GAG GTG AAG TCT Leu Thr Pro Glu Val Lys Ser mutation

  48. Difference between Meiosis and Mitosis

  49. Meiosis I Interphase Prophase I Metaphase I Anaphase I Telephase I

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