Biology - Chp 14 - Human Heredity - PowerPoint

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Biology - Chp 14 - Human Heredity - PowerPoint

  1. 1. Chapter 14 Human Heredity
  2. 2. 14-1 Human Heredity
  3. 3. <ul><li>Scientists once knew much less about humans then about other “model” organisms such as fruit flies and mice </li></ul><ul><li>With the completion of the Human Genome Project scientists are on verge of understanding human genetics at least as well as they understand that of some other organisms </li></ul>
  4. 4. Human Chromosomes <ul><li>To analyze chromosomes, cell biologists photograph cells in mitosis </li></ul><ul><li>Chromosomes are fully condensed and easiest to see during metaphase </li></ul>
  5. 5. Karyotype <ul><li>A picture of chromosomes arranged in order </li></ul>
  6. 6. <ul><li>We all began life when a haploid sperm fertilized a haploid egg carrying just ________ chromosomes each. </li></ul><ul><li>The _________________________ zygote or fertilized egg contained the full complement of __________ chromosomes </li></ul>23 Diploid 46
  7. 7. Sex Chromosomes <ul><li>Determine an individuals sex </li></ul><ul><li>Females: XX </li></ul><ul><li>Males: XY </li></ul><ul><li>The regular 44 chromosomes are known as autosomes </li></ul>
  8. 8. Q: Why are males & females born in a roughly 50:50 ratio? <ul><li>A: All egg cells carry a single _______ chromosome. However, half of all sperm carry an _______ chromosome, the other half carry a ________ chromosome </li></ul>X X Y
  9. 10. Human Traits <ul><li>In order to apply Mendelian genetics to humans, biologists must identify an inherited trait controlled by a single gene </li></ul><ul><li>Then, they have to study how the trait is passed from one generation to the next </li></ul>
  10. 11. Pedigree <ul><li>A chart which shows the relationship within a family </li></ul>
  11. 13. <ul><li>Most human traits are not coded for by single genes </li></ul><ul><li>Also, many traits are strongly influenced by environmental factors </li></ul><ul><ul><li>Ex.) average height has increased 10cm in the United States and Europe since 1800’s </li></ul></ul>
  12. 14. Polygenic Traits <ul><li>Traits coded for by many genes </li></ul><ul><li>Ex.) skin color, hair color </li></ul>
  13. 15. The Human Genome <ul><li>Our complete set of genetic information </li></ul><ul><li>Includes tens of thousands of genes </li></ul><ul><li>Until recently the identification of a human gene took years of work </li></ul>
  14. 16. <ul><li>Long generation times </li></ul><ul><li>Complex life cycle </li></ul><ul><li>Produce few offspring </li></ul>Humans aren’t easy test subjects
  15. 17. Blood Group Genes <ul><li>A number of genes are responsible for human blood groups, but the best known are the ABO and Rh blood groups </li></ul><ul><li>Rh blood groups </li></ul><ul><li>Rh+ (dominant) </li></ul><ul><li>Rh- (recessive) </li></ul>
  16. 18. Q: How do scientists identify recessive alleles that cause these disorders <ul><li>A: Compare affected persons genotype to normal persons </li></ul>
  17. 19. PKU – phenylketonuria <ul><li>Lack enzyme needed to break down phenylalanine </li></ul><ul><li>Found in milk and other foods </li></ul><ul><li>If newborn has PKU, phenylalanine may build up in the tissues during severe mental retardation </li></ul><ul><li>If newborns are tested early, they can be placed on a low phenylalanine diet which prevents most of the affects </li></ul><ul><li>PKU is caused by a recessive allele carried on chromosome 12 </li></ul>
  18. 20. PKU
  19. 21. Tay Sachs <ul><li>Autosomal recessive </li></ul><ul><li>Found mostly in Jewish families of central and eastern European ancestry </li></ul><ul><li>Results in nervous system breakdown and death in the first few years of life </li></ul><ul><li>There is no treatment, but there is a test prospective parents can take </li></ul>
  20. 22. Achondroplasia - dwarfism <ul><li>Never reach 4 feet 4 inches </li></ul><ul><li>Cartilage forms in such a way that the arms and legs end up being disproportionately short </li></ul><ul><li>1 in every 10,000 is affected </li></ul>
  21. 23. Huntington's <ul><li>Progressive loss of muscle control and mental function until death occurs </li></ul><ul><li>People with disease show no symptoms until they are in their 30’s and 40’s </li></ul>
  22. 24. Huntington's affect on the brain
  23. 25. Codominant <ul><li>Sickle cell disease </li></ul><ul><li>Affects 1 in 500 African Americans </li></ul>
  24. 26. From Gene to Molecule
  25. 27. Cystic Fibrosis (CF) <ul><li>Most common among people whose ancestors come from northern Europe </li></ul><ul><li>Caused by a recessive allele on chromosome 7 </li></ul><ul><li>Produce a thick heavy mucus that clogs their lungs and breathing passageways </li></ul><ul><li>Serious digestive problems </li></ul><ul><li>Only half survive into their 20’s </li></ul>
  26. 29. Sickle Cell Disease <ul><li>Characterized by the bent and twisted shape of the red blood cell </li></ul><ul><li>Sickle shaped red blood cell tend to get stuck in the capillaries </li></ul><ul><li>Produce physical weakness and damage to the brain, heart and spleen </li></ul><ul><li>Sometimes fatal </li></ul><ul><li>Change in just one DNA base </li></ul><ul><li>This change inserts amino acid valine in place of glutamic acid </li></ul><ul><li>Hemoglobin molecules stick together and form long chains that produce the characteristic shape of sickled cells </li></ul>
  27. 32. Q: Why do so many African Americans carry the sickle cell allele? <ul><li>A: Many African Americans have West Central African ancestry where malaria is a serious problem </li></ul><ul><li>People who are heterozygous for the sickle cell allele don’t get sickle cell and they don’t get malaria </li></ul>
  28. 33. Where malaria is common Where sickle cell is common
  29. 34. Dominant or Recessive <ul><li>It all depends on the nature of a genes protein product and its role in the cell </li></ul><ul><li>Ex.) In CF, one copy of the normal allele can supply cells with enough chloride channel proteins to function therefore the normal CF allele is considered ____________________ </li></ul>Dominant
  30. 36. 14-2 Human Chromosomes
  31. 37. <ul><li>A human diploid cell contains more than 6 billion nucleiotide pairs of DNA </li></ul><ul><li>Despite its size, all of this information is neatly packed into the 46 chromosomes present in every diploid cell </li></ul><ul><li>Each chromosome is like a library containing hundreds or even thousands of books </li></ul><ul><li>Biologists are many decades away from mastering the contents of these books, but they are learning just how many books there are and what they deal with </li></ul>
  32. 38. Sex Linked Genes <ul><li>Genes located on the sex chromosomes </li></ul><ul><li>Most found on the ________ chromosome </li></ul>X
  33. 39. Colorblindness <ul><li>Gene associated with color vision are located on the X chromosome </li></ul><ul><li>Affects 1 in 10 males </li></ul><ul><li>Affects 1 in 100 females </li></ul>
  34. 40. Q: Why the difference between the sexes? <ul><li>A: Males have ____________________________ X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive </li></ul><ul><li>In order for a woman to be affected, there must be __________________________ of the allele </li></ul>just one Two copies
  35. 41. Hemophilia <ul><li>A protein necessary for normal ______________________________is missing </li></ul><ul><li>1 in 10,000 males </li></ul><ul><li>People with hemophilia can bleed to death from minor cuts and may suffer from internal bleeding </li></ul><ul><li>Treated with normal clotting factors </li></ul>Blood clotting
  36. 42. Duchenne Muscular Dystrophy <ul><li>Results in progressive weakening and loss of skeletal muscle </li></ul><ul><li>Rarely live past early adulthood </li></ul><ul><li>In the U.S. 1 in 3000 males is born with Duchenne muscular dystrophy </li></ul><ul><li>Caused by a defective version of the gene that codes for a muscle protein </li></ul>
  37. 43. X-Chromosome Inactivation <ul><li>Q: If all you need is one X chromosome, what happens to the extra X chromosome in females? </li></ul><ul><li>A: one chromosome is randomly switched off </li></ul><ul><li>Forms a barr body – dense region in the nucleus </li></ul>
  38. 44. Calico Cats <ul><li>Fur color is on the X chromosome. Some areas have one color switched on, and others its switched off </li></ul>
  39. 45. nondisjunction <ul><li>When homologous chromosomes fail to separate – most common error in meiosis </li></ul>
  40. 46. <ul><li>If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes </li></ul>
  41. 48. Down Syndrome <ul><li>When nondisjunction happens and a baby is born with 3 copies of chromosome 21 </li></ul><ul><li>Trisomy 21 </li></ul><ul><li>1 in 800 in U.S. </li></ul><ul><li>Mild to severe retardation </li></ul><ul><li>Susceptible to many diseases </li></ul><ul><li>Increased frequency of birth defects </li></ul>
  42. 49. Down Syndrome
  43. 50. Turners Syndrome (female) <ul><li>Only inherit one X chromosome, and no Y </li></ul><ul><li>Genotype = XO </li></ul><ul><li>Women with Turner syndrome are sterile, their sex organs don’t properly develop at puberty </li></ul>
  44. 52. Klinefelters Syndrome (males) <ul><li>Inherit extra X chromosomes </li></ul><ul><li>Genotype = XXY </li></ul><ul><li>The extra X interferes with meiosis and usually prevents them from reproducing </li></ul><ul><li>Some cases XXXY or XXXXY </li></ul><ul><li>These abnormalities show us the role of Y in sex determination </li></ul><ul><ul><li>Even in combination with several X’s, the Y makes them male </li></ul></ul><ul><li>But if this Y is absent, the embryo develops into a female </li></ul>
  45. 54. 14-3 Human Molecular Genetics
  46. 55. Human DNA Analysis <ul><li>Way too much DNA to search through </li></ul><ul><li>Biologists search the volumes of the human genome using DNA sequences </li></ul>
  47. 56. Testing for alleles <ul><li>If two prospective parents suspect they might be carrying recessive alleles for a genetic disorder they can now get a test to determine the risk of passing that trait on to their children </li></ul><ul><ul><li>Use labeled DNA probes to detect specific sequences found in disease causing alleles </li></ul></ul><ul><ul><li>Looking at changes in restrictive enzyme cutting sites </li></ul></ul><ul><ul><li>Looking at differences in lengths of alleles </li></ul></ul>
  48. 57. DNA fingerprinting <ul><li>Analyzes sections of DNA that have little or no known function but vary widely from one individual to another </li></ul><ul><li>Used to settle paternity disputes </li></ul><ul><li>Convict criminals and overturn convictions </li></ul>
  49. 58. The Human Genome Project <ul><li>Advances in DNA sequencing technologies at the close of the twentieth century made it possible to begin sequencing entire genomes </li></ul><ul><li>At first, biologists worked on small genomes of viruses and bacteria </li></ul><ul><li>In 1990, scientists in the United States and other countries began the Human Genome Project </li></ul><ul><ul><li>An attempt to sequence all human DNA </li></ul></ul><ul><li>In 2000 scientists announced that the DNA sequence of the human genome was essentially complete </li></ul><ul><li>We estimate as little as 31,000 genes </li></ul><ul><ul><li>Fruit fly – 14,000 </li></ul></ul><ul><ul><li>C. elegans worm 20,000 </li></ul></ul><ul><li>Now the task is to figure out how so few genes make an organism as complex as us </li></ul>
  50. 59. Promoter <ul><li>Section of DNA that signals the start of a gene </li></ul><ul><li>Researchers are looking for genes that provide useful clues to some of the basic properties of life </li></ul><ul><li>Also looking for genetic information that may be useful in developing new drugs and treatment of disease </li></ul>
  51. 60. A Breakthrough for Everyone <ul><li>Data from the human genome project is posted on the internet on a daily basis </li></ul><ul><li>www.genome.gov </li></ul>
  52. 61. Gene Therapy <ul><li>Replacing an absent or faulty gene by a normal working gene </li></ul>
  53. 62. Ethical Issues in Human Genetics <ul><li>There are many questions which science will rapidly force society to come to grips with </li></ul><ul><li>If it’s just as easy to manipulate genes for personal preference then it is to cure a disease should we do it? </li></ul><ul><li>Our society will have to develop a thoughtful and ethical conscious of what should and shouldn’t be done with the human genome </li></ul>

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