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Chapter 14- Human Genetics


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Sex-linked traits, chromosome disorders, and more!

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Chapter 14- Human Genetics

  1. 1. Biology Copyright Pearson Prentice Hall Biology
  2. 2. 14–1 Human Heredity 14-1 Human Heredity Copyright Pearson Prentice Hall
  3. 3. Human Chromosomes Cell biologists analyze chromosomes by looking at karyotypes. Cells are photographed during mitosis. Scientists then cut out the chromosomes from the photographs and group them together in pairs. Copyright Pearson Prentice Hall
  4. 4. A picture of an individual’s chromosomes, arranged in homologous pairs, is called a karyotype. Copyright Pearson Prentice Hall Human Karyotype
  5. 5. Human Chromosomes Humans have 46 chromosomes. Two are called sex chromosomes, because they determine an individual's sex. •Females have two X chromosomes. •Males have one X chromosome and one Y chromosome. Copyright Pearson Prentice Hall
  6. 6. Human Chromosomes The other 44 chromosomes are known as autosomal chromosomes, or autosomes. Copyright Pearson Prentice Hall
  7. 7. Human Chromosomes All human egg cells carry a single X chromosome (23,X). Half of all sperm cells carry an X chromosome (23,X) and half carry a Y chromosome (23,Y). About half of the zygotes will be 46,XX (female) and half will be 46,XY (male). Copyright Pearson Prentice Hall
  8. 8. Human Chromosomes Males and females are born in a roughly 50 : 50 ratio because of the way in which sex chromosomes segregate during meiosis. Copyright Pearson Prentice Hall
  9. 9. Copyright Pearson Prentice Hall
  10. 10. Human Traits Human Traits In order to apply Mendelian genetics to humans, biologists must identify an inherited trait controlled by a single gene. They must establish that the trait is inherited and not the result of environmental influences. They have to study how the trait is passed from one generation to the next. Copyright Pearson Prentice Hall
  11. 11. Human Traits Pedigree Charts A pedigree chart shows the relationships within a family. Genetic counselors analyze pedigree charts to infer the genotypes of family members. Copyright Pearson Prentice Hall Active art
  12. 12. Human Traits A circle represents a female. A horizontal line connecting a male and a female represents a marriage. Copyright Pearson Prentice Hall A shaded circle or square indicates that a person expresses the trait. A square represents a male. A vertical line and a bracket connect the parents to their children. A circle or square that is not shaded indicates that a person does not express the trait.
  13. 13. Genes and the Environment Some obvious human traits are almost impossible to associate with single genes. Traits, such as the shape of your eyes or ears, are polygenic, meaning they are controlled by many genes. Many of your personal traits are only partly governed by genetics. Copyright Pearson Prentice Hall
  14. 14. Human Genes The human genome includes tens of thousands of genes. In 2003, the DNA sequence of the human genome was published. In a few cases, biologists were able to identify genes that directly control a single human trait such as blood type. Copyright Pearson Prentice Hall
  15. 15. Blood Group Genes Human blood comes in a variety of genetically determined blood groups. A number of genes are responsible for human blood groups. The best known are the ABO blood groups and the Rh blood groups. Copyright Pearson Prentice Hall
  16. 16. Human Genes The Rh blood group is determined by a single gene with two alleles—positive and negative. The positive (Rh+) allele is dominant, so individuals who are Rh+/Rh+ or Rh+/Rh are said to be Rh-positive. Individuals with two Rh- alleles are said to be Rh-negative. Copyright Pearson Prentice Hall
  17. 17. Human Genes ABO blood group •There are three alleles for this gene, IA, IB, and i. •Alleles IA and IB are codominant. Copyright Pearson Prentice Hall
  18. 18. Human Genes Individuals with alleles IA and IB produce both A and B antigens, making them blood type AB. Copyright Pearson Prentice Hall
  19. 19. Human Genes The i allele is recessive. Individuals with alleles IAIA or IAi produce only the A antigen, making them blood type A. Copyright Pearson Prentice Hall
  20. 20. Human Genes Individuals with IBIB or IBi alleles are type B. Copyright Pearson Prentice Hall
  21. 21. Human Genes Individuals who are homozygous for the i allele (ii) produce no antigen and are said to have blood type O. Copyright Pearson Prentice Hall
  22. 22. Copyright Pearson Prentice Hall
  23. 23. Recessive Alleles The presence of a normal, functioning gene is revealed only when an abnormal or nonfunctioning allele affects the phenotype. Many disorders are caused by autosomal recessive alleles. Copyright Pearson Prentice Hall
  24. 24. Copyright Pearson Prentice Hall
  25. 25. Dominant Alleles The effects of a dominant allele are expressed even when the recessive allele is present. Two examples of genetic disorders caused by autosomal dominant alleles are achondroplasia and Huntington disease. Copyright Pearson Prentice Hall
  26. 26. Copyright Pearson Prentice Hall
  27. 27. Codominant Alleles Sickle cell disease is a serious disorder caused by a codominant allele. Sickle cell is found in about 1 out of 500 African Americans. Copyright Pearson Prentice Hall
  28. 28. Copyright Pearson Prentice Hall
  29. 29. Sickle Cell Disease is characterized by the bent and twisted shape of the red blood cells. Copyright Pearson Prentice Hall
  30. 30. Hemoglobin is the protein in red blood cells that carries oxygen. In the sickle cell allele, just one DNA base is changed. As a result, the abnormal hemoglobin is less soluble than normal hemoglobin. Low oxygen levels cause some red blood cells to become sickle shaped. Copyright Pearson Prentice Hall
  31. 31. There are three phenotypes associated with the sickle cell gene. Homozygous dominant- normal Heterozygous dominant- healthy with malaria resistance Homozygous recessive- sickle cell Sickle cell alleles are considered codominant. Copyright Pearson Prentice Hall
  32. 32. Malaria and the Sickle Cell Allele Regions where malaria is common Regions where the sickle cell allele is common Because the sickle cell allele gives resistance to malaria it persists in areas where malaria is a problem. Copyright Pearson Prentice Hall
  33. 33. In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder. Copyright Pearson Prentice Hall
  34. 34. From Gene to Molecule Cystic Fibrosis Cystic fibrosis is caused by a recessive allele. Sufferers of cystic fibrosis produce a thick, heavy mucus that clogs their lungs and breathing passageways. Copyright Pearson Prentice Hall
  35. 35. The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein. Copyright Pearson Prentice Hall
  36. 36. From Gene to Molecule Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane. Copyright Pearson Prentice Hall
  37. 37. The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus. Copyright Pearson Prentice Hall
  38. 38. These diseases are autosomal recessive because you only need one functional gene to make a good protein. FF Ff ff Copyright Pearson Prentice Hall Makes good protein Makes some good protein and some that doesn’t work Makes protein that doesn’t work
  39. 39. 14–2 Human Chromosomes 14-2 Human Chromosomes Copyright Pearson Prentice Hall
  40. 40. Sex-Linked Genes •The X chromosome and the Y chromosomes determine sex. •Genes located on sex chromosomes are called sex-linked genes. •More than 100 sex-linked genetic disorders have now been mapped to the X chromosome. Copyright Pearson Prentice Hall
  41. 41. Sex-Linked Genes The Y chromosome is much smaller than the X chromosome and appears to contain only a few genes. X Chromosome Copyright Pearson Prentice Hall Duchenne muscular dystrophy Melanoma X-inactivation center X-linked severe combined immunodeficiency (SCID) Colorblindness Hemophilia Y Chromosome Testis-determining factor
  42. 42. For a recessive allele to be expressed in females, there must be two copies of the allele, one on each of the two X chromosomes. Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive. Copyright Pearson Prentice Hall
  43. 43. Colorblindness Three human genes associated with color vision are located on the X chromosome. In males, a defective version of any one of these genes produces colorblindness. Copyright Pearson Prentice Hall
  44. 44. Copyright Pearson Prentice Hall Possible Inheritance of Colorblindness Allele
  45. 45. Hemophilia •The X chromosome also carries genes that help control blood clotting. A recessive allele in either of these two genes may produce hemophilia. • In hemophilia, a protein necessary for normal blood clotting is missing. •Hemophiliacs can bleed to death from cuts and may suffer internal bleeding if bruised. Copyright Pearson Prentice Hall
  46. 46. Duchenne Muscular Dystrophy •Duchenne muscular dystrophy is a sex-linked disorder that results in the weakening and loss of skeletal muscle. • It is caused by a defective version of the gene that codes for a muscle protein. Copyright Pearson Prentice Hall
  47. 47. Recessive traits from genes on the X-chromosome, like color blindness and hemophilia, are much more common in males.
  48. 48. X-Chromosome Inactivation •British geneticist Mary Lyon discovered that in female cells, one X chromosome is randomly switched off. •The inactive X chromosome forms a dense region in the nucleus known as a Barr body. • Barr bodies are generally not found in males because their single X chromosome is still active. Copyright Pearson Prentice Hall
  49. 49. GENETIC DISORDERS caused by NON-DISJUNCTION •The most common error in meiosis occurs when homologous chromosomes fail to separate. Copyright Pearson Prentice Hall
  50. 50. GENETIC DISORDERS caused by NON-DISJUNCTION Copyright Pearson Prentice Hall
  51. 51. GENETIC DISORDERS caused by NON-DISJUNCTION •This is known as nondisjunction, which means, “not coming apart.” •nondisjunction causes abnormal numbers of chromosomes Copyright Pearson Prentice Hall
  52. 52. Down Syndrome •If two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with three copies of a chromosome. •Down syndrome involves three copies of chromosome 21. Copyright Pearson Prentice Hall
  53. 53. Chromosomal Disorders Down syndrome produces mild to severe mental retardation. It is characterized by: • increased susceptibility to many diseases •higher frequency of some birth defects Down Syndrome Karyotype Copyright Pearson Prentice Hall
  54. 54. Sex Chromosome Disorders • In females, nondisjunction can lead to Turner’s syndrome. •A female with Turner’s syndrome usually inherits only one X chromosome (karyotype 45,X). •Women with Turner’s syndrome are sterile. Copyright Pearson Prentice Hall
  55. 55. Chromosomal Disorders In males, nondisjunction causes Klinefelter’s syndrome (karyotype 47,XXY). The extra X chromosome interferes with meiosis and usually prevents these individuals from reproducing. Copyright Pearson Prentice Hall
  56. 56. The X chromosome contains genes necessary for survival.
  57. 57. 14–3 Human Molecular Genetics 14-3 Human Molecular Genetics Copyright Pearson Prentice Hall
  58. 58. Human DNA Analysis • There are roughly 6 billion base pairs in your DNA. •Biologists search the human genome using sequences of DNA bases. Copyright Pearson Prentice Hall
  59. 59. Genetic tests are available for hundreds of disorders. DNA testing can pinpoint the exact genetic basis of a disorder. Copyright Pearson Prentice Hall
  60. 60. •DNA fingerprinting analyzes the DNA repeats which make a unique pattern for each individual. •Only identical twins are genetically identical. •DNA samples can be obtained from blood, sperm, and hair strands with tissue at the base. Copyright Pearson Prentice Hall
  61. 61. Human DNA Analysis Chromosomes contain large amounts of DNA called repeats that do not code for proteins. This DNA pattern varies from person to person. Copyright Pearson Prentice Hall Active art
  62. 62. Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. Copyright Pearson Prentice Hall
  63. 63. DNA fragments are separated using gel electrophoresis. Fragments containing repeats are labeled. This produces a series of bands— the DNA fingerprint. Copyright Pearson Prentice Hall
  64. 64. Copyright Pearson Prentice Hall DNA Fingerprint
  65. 65. In 1990, scientists in the United States and other countries began the Human Genome Project. The Human Genome Project is an ongoing effort to analyze the human DNA sequence. In June 2000, a working copy of the human genome was essentially complete. Copyright Pearson Prentice Hall
  66. 66. Research groups are analyzing the DNA sequence, looking for genes that may provide clues to the basic properties of life. Biotechnology companies are looking for information that may help develop new drugs and treatments for diseases. Copyright Pearson Prentice Hall
  67. 67. A Breakthrough for Everyone •Data from publicly supported research on the human genome have been posted on the Internet on a daily basis. •You can read and analyze the latest genome data. Copyright Pearson Prentice Hall
  68. 68. In gene therapy, an absent or faulty gene is replaced by a normal, working gene. The body can then make the correct protein or enzyme, eliminating the cause of the disorder. Copyright Pearson Prentice Hall
  69. 69. Viruses are often used because of their ability to enter a cell’s DNA. Virus particles are modified so that they cannot cause disease. Normal hemoglobin gene Genetically engineered virus Copyright Pearson Prentice Hall
  70. 70. A DNA fragment containing a replacement gene is spliced to viral DNA. Bone marrow cell Copyright Pearson Prentice Hall Chromosomes Nucleus Genetically engineered virus
  71. 71. The patient is then infected with the modified virus particles, which should carry the gene into cells to correct genetic defects. Copyright Pearson Prentice Hall
  72. 72. Copyright Pearson Prentice Hall 14–1 A chromosome that is not a sex chromosome is know as a(an) a. autosome. b. karyotype. c. pedigree. d. chromatid.
  73. 73. Copyright Pearson Prentice Hall 14–1 Whether a human will be a male or a female is determined by which a. sex chromosome is in the egg cell. b. autosomes are in the egg cell. c. sex chromosome is in the sperm cell. d. autosomes are in the sperm cell.
  74. 74. Copyright Pearson Prentice Hall 14–1 Mendelian inheritance in humans is typically studied by a. making inferences from family pedigrees. b. carrying out carefully controlled crosses. c. observing the phenotypes of individual humans. d. observing inheritance patterns in other animals.
  75. 75. Copyright Pearson Prentice Hall 14–1 An individual with a blood type phenotype of O can receive blood from an individual with the phenotype a. O. b. A. c. AB. d. B.
  76. 76. Copyright Pearson Prentice Hall 14–1 The ABO blood group is made up of a. two alleles. b. three alleles. c. identical alleles. d. dominant alleles.
  77. 77. Copyright Pearson Prentice Hall 14–2 The average human gene consists of how many base pairs of DNA? a. 3000 b. 300 c. 20 d. 30,000
  78. 78. Copyright Pearson Prentice Hall 14–2 Which of the following genotypes indicates an individual who is a carrier for colorblindness? a. XCX b. XCXc c. XcY d. XCY
  79. 79. Copyright Pearson Prentice Hall 14–2 Colorblindness is much more common in males than in females because a. the recessive gene on the male’s single X chromosome is expressed. b. genes on the Y chromosome make genes on the X chromosome more active. c. females cannot be colorblind. d. colorblindness is dominant in males and recessive in females.
  80. 80. Copyright Pearson Prentice Hall 14–2 The presence of a dense region in the nucleus of a cell can be used to determine the a. sex of an individual. b. blood type of an individual. c. chromosome number of an individual. d. genotype of an individual.
  81. 81. Copyright Pearson Prentice Hall 14–2 Nondisjunction occurs during a. meiosis I. b. mitosis. c. meiosis II. d. between meiosis I and II.
  82. 82. Copyright Pearson Prentice Hall 14–3 DNA fingerprinting analyzes sections of DNA that have a. Little or no known function but are identical from one individual to another. b. little or no known function but vary widely from one individual to another. c. a function and are identical from one individual to another.
  83. 83. Copyright Pearson Prentice Hall 14–3 DNA fingerprinting uses the technique of a. gene therapy. b. allele analysis. c. gel electrophoresis. d. gene recombination.
  84. 84. Copyright Pearson Prentice Hall 14–3 Repeats are areas of DNA that a. do not code for proteins. b. code for proteins. c. are identical from person to person. d. cause genetic disorders.
  85. 85. Copyright Pearson Prentice Hall 14–3 Data from the human genome project is available a. only to those who have sequenced the DNA. b. to scientists who are able to understand the data. c. by permission to anyone who wishes to do research. d. to anyone with Internet access.
  86. 86. Copyright Pearson Prentice Hall 14–3 Which statement most accurately describes gene therapy? a. It repairs the defective gene in all cells of the body. b. It destroys the defective gene in cells where it exists. c. It replaces absent or defective genes with a normal gene. d. It promotes DNA repair through the use of enzymes.