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09 Lecture Ppt

  1. 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 Patterns of Genetic Inheritance
  2. 2. Gregor Mendel Deduced Laws of Inheritance 9-
  3. 3. 9.1 A blending model of inheritance existed prior to Mendel <ul><li>Austrian monk Gregor Mendel developed the fundamental laws of heredity after performing a series of experiments with pea plants </li></ul>9-
  4. 4. Figure 9.1 Gregor Mendel examining a pea plant 9-
  5. 5. 9.2 Mendel designed his experiments well <ul><li>Figure 9.2A Garden pea anatomy and the </li></ul><ul><li>cross-pollination procedure Mendel used </li></ul>9-
  6. 6. Figure 9.2B Garden pea traits and crosses studied by Mendel 9-
  7. 7. Single-Trait Crosses Reveal Units of Inheritance and the Law of Segregation 9-
  8. 8. 9.3 Mendel’s law of segregation describes how gametes pass on traits <ul><li>The law of segregation states: </li></ul><ul><ul><li>Each individual has two factors for each trait </li></ul></ul><ul><ul><li>The factors segregate (separate) during the formation of the gametes </li></ul></ul><ul><ul><li>Each gamete contains only one factor from each pair of factors </li></ul></ul><ul><ul><li>Fertilization gives each new individual two factors for each trait </li></ul></ul>9-
  9. 9. Figure 9.3 Monohybrid cross done by Mendel 9-
  10. 10. 9.4 The units of inheritance are alleles of genes <ul><li>Traits are controlled by alleles - alternate forms of a gene </li></ul><ul><ul><li>Found on homologous chromosomes at a particular gene locus </li></ul></ul><ul><li>The dominant allele masks the expression of the other allele - the recessive allele </li></ul><ul><li>Genotype refers to the alleles an individual receives at fertilization </li></ul><ul><ul><li>Homozygous - an organism has two identical alleles at a gene locus </li></ul></ul><ul><ul><li>Heterozygous - an organism has two different alleles at a gene locus </li></ul></ul><ul><li>Phenotype - the physical appearance of the individual. </li></ul>9-
  11. 11. 9-
  12. 12. Figure 9.4 Occurrence of alleles on homologous chromosomes 9-
  13. 13. Two-Trait Crosses Support the Law of Independent Assortment 9-
  14. 14. 9.5 Mendel’s law of independent assortment describes inheritance of multiple traits <ul><li>The law of independent assortment states the following: </li></ul><ul><ul><li>Each pair of factors separates (assorts) independently (without regard to how the others separate) </li></ul></ul><ul><ul><li>All possible combinations of factors can occur in the gametes </li></ul></ul>9-
  15. 15. Figure 9.5 Dihybrid cross done by Mendel 9-
  16. 16. 9.6 Mendel’s results are consistent with the laws of probability <ul><li>Figure 9.6 Use of Punnett square to calculate probable events </li></ul>9-
  17. 17. 9.7 Testcrosses support Mendel’s laws and indicate the genotype <ul><li>Testcross - intentional breeding in order to determine underlying genotypes </li></ul><ul><ul><li>One-trait Testcross - When a heterozygous individual is crossed with one that is homozygous recessive, the results are always a 1:1 phenotypic ratio </li></ul></ul><ul><ul><li>Two-trait Testcross - when an individual is heterozygous for two traits is crossed with one that is recessive for the traits, the offspring have a 1:1:1:1 phenotypic ratio </li></ul></ul>9-
  18. 18. Figure 9.7A One-trait testcross, when the individual with the dominant phenotype is heterozygous 9-
  19. 19. Figure 9.7B One-trait testcross when the individual with the dominant phenotype is homozygous 9-
  20. 20. Mendel’s Laws Apply to Humans 9-
  21. 21. 9.8 Pedigrees can reveal the patterns of inheritance <ul><li>Some genetic disorders are medical conditions inherited from parents </li></ul><ul><li>Some may be due to the inheritance of abnormal alleles on autosomal chromosomes - all the chromosomes except the sex chromosomes </li></ul><ul><ul><li>Carriers - those individuals that carry the abnormal allele but do not express it </li></ul></ul>9-
  22. 22. Figure 9.8A Autosomal recessive pedigree 9-
  23. 23. Figure 9.8B Autosomal dominant pedigree 9-
  24. 24. 9.9 Some human genetic disorders are autosomal recessive <ul><li>Tay-Sachs Disease - uncontrollable seizures, and paralysis prior to dying </li></ul><ul><ul><li>Results from a lack of the enzyme Hex A </li></ul></ul><ul><li>Cystic Fibrosis - most common lethal genetic disease of Caucasians in the U.S. </li></ul><ul><ul><li>Genetic testing for the recessive allele is possible </li></ul></ul><ul><li>Phenylketonuria - most commonly inherited metabolic disorder affecting nervous system </li></ul><ul><ul><li>Many diet products have warnings that they contain phenylalanine </li></ul></ul><ul><li>Sickle-cell Disease - genotype Hb S Hb S has many symptoms from anemia to heart failure </li></ul><ul><ul><li>Individuals who are Hb A Hb S have sickle-cell trait </li></ul></ul>9-
  25. 25. 9.10 Some human genetic disorders are autosomal dominant <ul><li>Neurofibromatosis - many children with neurofibromatosis have learning disabilities and are hyperactive </li></ul><ul><li>Huntington disease - a neurological disorder that leads to progressive degeneration of brain cells </li></ul><ul><li>Achondroplasia - a common form of dwarfism associated with a defect in the growth of long bones </li></ul>9-
  26. 26. APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES 9.11 Genetic disorders may now be detected early on <ul><li>Testing Fetal Cells </li></ul><ul><ul><li>Amniocentesis - long needle withdraws a small amount of the fluid that surrounds the fetus and contains a few fetal cells </li></ul></ul><ul><ul><li>Chorionic Villi Sampling (CVS) - tube is inserted through the vagina into the uterus and fetal cells are obtained by suction </li></ul></ul><ul><li>Testing the Embryo </li></ul><ul><ul><li>A single cell can be removed from the 8-celled embryo and subjected to preimplantation genetic diagnosis (PGD) </li></ul></ul><ul><li>Testing the Egg </li></ul><ul><ul><li>Polar bodies (nonfunctional cells produced during egg formation) receive a haploid number of chromosomes </li></ul></ul><ul><ul><li>When a woman is heterozygous for a recessive genetic disorder, about half the polar bodies have received the mutated allele, while the egg has received the normal allele </li></ul></ul>9-
  27. 27. Figure 9.11A Prepregnancy testing of an embryo 9-
  28. 28. Figure 9.11B Prepregnancy testing of an egg 9-
  29. 29. Complex Inheritance Patterns Extend the Range of Mendelian Analysis 9-
  30. 30. 9.12 Incomplete dominance still follows the law of segregation <ul><li>Incomplete dominance - heterozygote has an intermediate phenotype between that of either homozygote </li></ul>9-
  31. 31. Figure 9.12 Incomplete dominance 9-
  32. 32. 9.13 A gene may have more than two alleles <ul><li>Multiple alleles - gene has several allelic forms </li></ul><ul><ul><li>Example: blood type is determined by multiple alleles </li></ul></ul><ul><ul><ul><li>I A = A antigen on red blood cells </li></ul></ul></ul><ul><ul><ul><li>I B = B antigen on red blood cells </li></ul></ul></ul><ul><ul><ul><li>i = Neither A nor B antigen on red blood cells </li></ul></ul></ul><ul><ul><li>Possible phenotypes and genotypes for blood type: </li></ul></ul><ul><li>This is an example of codominance because both I A and I B are fully expressed </li></ul>9-
  33. 33. 9.14 Several genes and the environment can influence a single multifactorial characteristic <ul><li>Polygenic inheritance occurs when a trait is governed by two or more genes </li></ul><ul><ul><li>Multifactorial traits - controlled by polygenes subject to environmental influences </li></ul></ul>9-
  34. 34. Figure 9.14 Polygenic inheritance: Dark dots stand for dominant alleles; the shading stands for environmental influences 9-
  35. 35. 9.15 One gene can influence several characteristics <ul><li>Pleiotropy - when a single gene has more than one effect </li></ul>9-
  36. 36. Figure 9.15A Marfan syndrome illustrates the multiple effects a single human gene can have 9-
  37. 37. Chromosomes Are the Carriers of Genes 9-
  38. 38. 9.16 Traits transmitted via the X chromosome have a unique pattern of inheritance <ul><li>X-linked alleles have a different pattern of inheritance than autosomal alleles </li></ul><ul><ul><li>The Y chromosome cannot offset the inheritance of an X-linked recessive allele </li></ul></ul><ul><li>Affected males always receive their X-linked recessive mutant allele from the female parent </li></ul>9-
  39. 39. Figure 9.16 X-linked inheritance 9-
  40. 40. 9.17 Humans have X-linked disorders <ul><li>Color Blindness - the alleles for the red- and green-sensitive proteins are on the X chromosome </li></ul><ul><li>Muscular Dystrophy - occurs in males but the recessive allele remains in the population through passage from mother to daughter </li></ul><ul><li>Hemophilia - 1 in 10,000 males is affected by both external and internal bleeding </li></ul>9-
  41. 41. Figure 9.17 X-linked recessive pedigree 9-
  42. 42. 9.18 The genes on one chromosome form a linkage group <ul><li>Gene linkage - the existence of several genes on the same chromosome </li></ul><ul><ul><li>Genes on a single chromosome form a linkage group because they tend to be inherited together </li></ul></ul>9-
  43. 43. Figure 9.18 A simplified map of the genes on chromosome 2 of Drosophila 9-
  44. 44. 9.19 Frequency of recombinant gametes maps the chromosomes <ul><li>A linkage map can also be called a chromosome map because it tells the order of gene loci on chromosomes </li></ul>9-
  45. 45. Figure 9.19 Example of incomplete linkage 9-
  46. 46. APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES 9.20 Thomas Hunt Morgan is commonly called “the fruit fly guy” <ul><li>In 1908, Morgan began experimenting with the fruit fly ( Drosophila melanogaster ) </li></ul>9-
  47. 47. Connecting the Concepts: Chapter 9 <ul><li>The first of Mendel’s laws tells us that an individual has two alleles, but the gametes have only one allele for every trait </li></ul><ul><ul><li>The second law tells us that the gametes have all possible combinations of alleles </li></ul></ul><ul><li>Polygenic inheritance and X-linked inheritance extend the range of Mendelian analysis </li></ul><ul><ul><li>Males are more apt than females to display an X-linked disorder </li></ul></ul><ul><li>Genes do have loci on the chromosomes, but today we know that genes are composed of DNA </li></ul>9-