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