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Chapter 14

Chapter 14. The Human Genome. 14-1 Human Heredity. Human Chromosomes Can be visualized with a karyotype A karyotype shows the number and type of chromosomes. Humans have 46 chromosomes Sex chromosomes: 2 Autosomal chromosomes ( autosomes ): 44. Human Traits.

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Chapter 14

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  1. Chapter 14 The Human Genome

  2. 14-1 Human Heredity • Human Chromosomes • Can be visualized with a karyotype • A karyotype shows the number and type of chromosomes

  3. Humans have 46 chromosomes • Sex chromosomes: 2 • Autosomal chromosomes (autosomes): 44

  4. Human Traits • Pedigree chart- a map of a characteristic’s presence in related individuals

  5. Dominant? Recessive? Female Male

  6. Dominant? Recessive? Female Male

  7. ? Dominant? Recessive? Female Male

  8. What determines a trait? • Many characteristics can not be traced on a pedigree chart: • Most physical traits in humans are polygenic • The environment can influence phenotype

  9. Universal Donor- O • Universal Recipient- AB • Rh factor (Rhesus monkey)- either positive or negative • Rh+ phenotype = Rh+/Rh+ or Rh+/Rh- genotype • Rh- phenotype = Rh-/Rh- genotype

  10. Autosomal recessive disorders • PKU (phenylketonuria)- lack an enzyme to break down phenylalanine (an amino acid found in milk and other foods) • Can cause mental retardation • Chromosome # 12

  11. Autosomal recessive disorders • Tay-Sachs disease- predominant in Jewish families • Nervous system breakdown and death in first few years

  12. Autosomal recessive disorders • Cystic Fibrosis- Excess mucus in lungs, digestive tract, liver. More susceptible to infections

  13. Dominant disorders • Achondroplasia- dwarfism • Caused by a dominant gene Huntington’s Disease- nervous system disorder, causes progressive loss of motor control and mental function. Symptoms appear in 30s

  14. Codominant disorders • Sickle Cell Disease- red blood cells are sickle shaped. They get stuck in capillaries and stop the passage of blood. It causes physical weakness and damage to brain and heart.

  15. From Gene to Molecule • What causes genetic disorders? • A change (mutation) in the DNA

  16. From Gene to Molecule • Cystic Fibrosis (CF)- caused by a deletion of three bases on chromosome 7 in the middle of a sequence for a protein. A Phenylalanine amino acid is missing. This protein allows chloride ions to pass across membranes. • Heterozygous- asymptomic, they produce enough of the protein.

  17. From Gene to Molecule • Sickle Cell Disease- a one base pair change of thymine to adenine. Amino acid glutamic acid is changed to valine.

  18. Malaria- a parasitic disease common in West Africa • Sickle Cell • Homozygous dominant- susceptible to malaria • Heterozygous- resistant to malaria • Homozygous recessive- sickle cell disease

  19. 14-2 Human Chromosomes • 97% of human DNA does not code for a protein. Average gene length is 3,000 base pairs • Chromosome 22 • 545 genes, mutations can cause leukemia, and tumors of nervous system Chromosome 23 225 genes, amyotrophic lateral sclerosis (ALS), Lou Gehrig’s disease

  20. Sex-Linked Genes • Sex-Linked Genes- disorders found on the X or Y chromosome. • X linked disorders- more than 100 • Y linked disorders- very few

  21. Sex-Linked Genes • Colorblindness- defect on the X chromosome • Red-green colorblindness- 1 in 10 males in the US, 1 in 100 females

  22. Sex-Linked Genes • Males have only one X chromosome. Any mutation is expressed. There are no heterozygous genotypes.

  23. Sex-Linked Genes • Hemophilia- a protein necessary for blood clotting is missing. The gene is carried on the X chromosome. • 1 in 10,000 males have hemophilia • Can be treated with injections of clotting proteins produced by recombinant DNA technology.

  24. Sex-Linked Genes • Duchenne Muscular Dystrophy- weakening and loss of muscle.

  25. X- Chromosome Inactivation • Females have two X chromosomes • One is randomly switched off • This forms a Barr body

  26. In cats the X chromosome controls part of the coat color. Orange and black colors are on the same chromosome.

  27. Chromosomal disorders • Nondisjunction- chromosomes fail to separate in meiosis.

  28. Chromosomal disorders • Down syndrome- mild to severe mental retardation • Caused by trisomy of chromosome 21

  29. Down syndrome

  30. Sex Chromosome Disorders • No X or Y- fatal- fetus does not develop • Turner’s syndrome- one X, females are sterile, sexual organs do not develop • Klinefelter’s syndrome- males with extra X, XXY,

  31. 14-3 Human Molecular Genetics • Human DNA Analysis • There are genetic tests for CF and Tay-Sachs disease • How do they work?

  32. Cystic Fibrosis (CF)- caused by a deletion of three bases on chromosome 7 in the middle of a sequence for a protein. A Phenylalanine amino acid is missing. • XXX-XXX-XXX-XXX-AAA-XXX-XXX-XXX Normal • XXX-XXX-XXX-XXX-XXX-XXX-XXX CF • How can we distinguish between the two types of DNA with our molecular tool kit?

  33. AGA-CTC-TTT-GAG-AAA-CCG-CCG-ATA • AGA-CTC-TTT-GAG-CCG-CCG-ATA • Restriction enzyme: • cuts at GAAACC into GAAA CC • AGA-CTC-TTT-GAG-AAA-CCG-CCG-ATA • AGA-CTC-TTT-GAG-CCG-CCG-ATA

  34. How can we separate the DNA? • AGA-CTC-TTT-GAG-AAA-CCG-CCG-ATA • AGA-CTC-TTT-GAG-CCG-CCG-ATA

  35. How can we separate the DNA? • AGA-CTC-TTT-GAG-AAA-CCG-CCG-ATA • AGA-CTC-TTT-GAG-CCG-CCG-ATA • Gel Electrophoresis

  36. DNA Fingerprinting • DNA Fingerprinting- used to identify individuals based on differences in DNA

  37. DNA Fingerprinting • Most functional genes are identical in humans • Differences in DNA often occur in the 97% of DNA that does not make functional proteins. Much of our DNA is repeated segments of the same sequence. • XXXXXX-gene-XXXX-gene-XXXXXX-gene-XXXX • XXXX-gene-XXXX-gene-XXXXXXXXXX-gene-XX

  38. DNA Fingerprinting • XXXXXX-gene-XXXX-gene-XXXXXX-gene-XXXX • XXXX-gene-XXXX-gene-XXXXXXXXXX-gene-XX • Restriction enzymes cut at regions that are highly variable. Gel electrophoresis separates the DNA based on size. • Everyone has a unique pattern of fragments that are produced when their DNA is cut by restriction enzymes.

  39. The Human Genome Project • E. coli has 4.6 million base pairs • Humans have a total of 6 billion base pairs • 3 billion in a haploid cell 1990 The Human Genome Project began purpose was to sequence the entire human genome

  40. The Human Genome Project • Working copy- 2000 • Complete copy- 2003 • Public vs Private debate • Should DNA be patented? • Craig Venter- Celera Genomics Shotgun sequencing- cut DNA into random fragments, sequence the fragments, use computers to put together the pieces

  41. The Human Genome Project- Findings • Very few genes- 35,000 • E. coli : 14,000; round worm: 20,000 Looked for promoter sequences to find genes

  42. Gene Therapy • Gene Therapy- an absent or faulty gene is replaced by a normal, working gene • First attempted in 1990. First success- in 1999 a young French girl has her bone marrow removed, modified, and reinserted.

  43. Gene Therapy • 1. A virus is modified with the correct DNA sequence for a protein.

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