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Chapter 14

Chapter 14. The Human Genome. Human Chromosomes. Our Focus this Chapter: Karyotype Sex Determination Genes and the Environment Genes and Inheritance Polygenic Dominant vs. Recessive Pedigree Charts and Punnett Squares Human Genes Inheritance Patterns

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Chapter 14

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  1. Chapter 14 The Human Genome

  2. Human Chromosomes Our Focus this Chapter: • Karyotype • Sex Determination • Genes and the Environment • Genes and Inheritance • Polygenic • Dominant vs. Recessive • Pedigree Charts and Punnett Squares • Human Genes • Inheritance Patterns • Gene Inheritance: Polygenic, dominant, recessive, codominant, sex-linked, linked • Chromosomal Disorders

  3. Karyotype • Autosomes: Body chromosomes (#1-22) • Sex Chromosomes • Male or Female? (hint: the one in your notes is different from this one)#23

  4. Fertilization Chart • Haploid (23) • Diploid (46)

  5. Sex Determination • Punnett Square • Probability: 50% male 50% female

  6. Human Genes • What is a gene? A segment of DNA coding for a protein (phenotype)

  7. Genes and the Environment Influences on Gene Expression (phenotype) • Nature vs. Nurture • Gene expression • Nutrition • Exercise • Stress • epigenetics

  8. Genes and Inheritance • Polygenic Traits: -Multiple genes on different chromosomes affecting one trait • Combination of dominant and recessive Ex: Hair color, Eye Color, Height • Multiple Allele • More than 2 possible alleles, in the population,for 1 genes • Each individual still only has 2 alleles Ex. Blood Type IA, IB,i

  9. Genes and Inheritance Dominant vs. Recessive Recessive alleles are masked in the presence of a dominant allele Incomplete Dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele. Codominant -(blood type)

  10. Pedigree Chart(traces family history) Figure 14-3 A Pedigree Section 14-1 A circle represents a female. A square represents a male. A vertical line and a bracket connect the parents to their children. A horizontal line connecting a male and female represents a marriage. A half-shaded circle or square indicates that a person is a carrier of the trait. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait. Use a Punnett Square (determines probability) to illustrate the genetic probability of the first couple’s offspring. Problem Solving: p343

  11. Blood Type • Multiple Allele (A, B, O) • Codominant(A and B) • Dominant/Recessive (A & B are dominant over O)

  12. Blood Type in the Human Population

  13. Human Genes • Blood Type • Disorders • Gene • Autosomal • Recessive • Dominant • Codominant • Sex-linked • Recessive • Chromosomal

  14. Autosomal Recessive • Both copies of the gene must be the recessive allele • Represented by a lower case letter • Albinism – • Phenylketonuria – • Tay Sachs – • Galactosemia – • Cystic Fibrosis – Chart p345

  15. Autosomal Recessive Albinism Genotype: aa Expression: • Missing Melanin (pigment) • Lack of color in skin, hair and eyes • Vision impairment Treatment: • Glasses, eye surgery

  16. Autosomal Recessive Phenylketonuria (PKU) Genotype: (chromosome 12) pp Expression: • Missing phenylalanine hydroxylase • Inability to process phenylalanine • Abnormal pigment • Mental retardation Treatment • Specialized diet low in phenylalanine

  17. Autosomal Recessive Tay Sachs Genotype: (chromosome 15) tt Expression: • Lack enzyme hexosaminidase A • Lipid accumulation in brain, blindness, mental deficiency, death Treatment: • None • Genetic testing available

  18. Autosomal Recessive Cystic Fibrosis Genotype: (chromosome 12) cc Expression: • Deletion of 3 bases = loss of phenylalanine in gene • Abnormal chloride channels cannot be transported to membrane • No chloride channels causes airways to become clogged with thick mucous Treatment • Drug therapies and lung therapies extend lives

  19. Autosomal Dominant • Only one copy of the genes is necessary to exhibit the trait • Represented by a capital letter • Achondroplasia • Huntington’s Disease • Hypercholesterolemia

  20. Autosomal Dominant Huntington Disease Genotype: (chromosome 4) Hh Expression: • Extensive repetition of CAG on DNA • Adult-onset • Neurological Symptoms Include: • Disorientation or confusion, Loss of judgment, Loss of memory, Speech changes • Death (usually by 50) Treatment • Medications used to slow symptoms Singer/Songwriter Woody Guthrie “This Land is Your Land”

  21. Autosomal Dominant Achondroplasia (dwarfism) Genotype: (chromosome 4) Aa Expression: • Problems with bone ossification of long bones • Effect growth • Average head and torso with shortened arms and legs Fun Fact • 80% of Achondroplasia cases are new mutations primarily from men >35

  22. Codominant • 2 alleles can be expressed at the same time • Sickle Cell Anemia HA – normal allele HS - sickle cell HA HA , HA HS, HS HS

  23. Sickle Cell Anemia

  24. Distribution of Sickle Cell Anemia vs. Malaria Sickle Cell Malaria 10% of African Americans and 40% of populations in Africa and Asia carry the gene for Sickle Cell Anemia

  25. From gene to molecule DNA normal hemoglobin CAC GTG GAC TGA GGA CTC CTC mRNA Amino acid sequence (p303) DNA Sickle Cell Anemia CAC GTG GAC TGA GGA CAC CTC mRNA amino acid GUG CAC CUG ACU CCU GAG GAG Val – His – Leu – Thr – Pro – Glu – Glu… 1 2 3 4 5 6 7 …146 GUG CAC CUG ACU CCU GUG GAG Val – His – Leu – Thr – Pro–VAL – Glu… 1 2 3 4 5 6 7 …146

  26. Sex-Linked Genes • Genes that are found on the X (or Y) chromosome and are linked to a person’s gender. • Recessive type seems to disappear only to reappear later. • Males have a higher chance of having sex-linked disorders. • They only need one copy of the gene in order to express it. • Examples: colorblindness, hemophilia, Duchenne Musclar Dystropy

  27. Sex-linked Recessive Red-Green Colorblindness • Normal Vision • would be able to see all #s • XCXC, XCXc • XCY • A colorblind person • could see 25 and 56 • XcXc • XcY

  28. Sex-linked Recessive • Red-Green Colorblindness

  29. Sex-linked Recessive Hemophilia Genotype: XhXh, XhY carrier: XHXh Expression: • Lack of clotting factors for blood • Bleeder’s disease • Can die if bleeding is left untreated Treatment: • Clotting factor replacement • Gene therapy* (what is gene therapy?)

  30. Royal Family and Hemophilia

  31. Sex-linked Recessive Duchenne Muscular Dystrophy Genotype: XmXm, XmY carrier: XMXm Expression: • Defective protein in muscle (dystrophin) • Fatigue • Learning difficulties (IQ can be below 75) • Muscle weakness • Eventually, inability to walk and breathe • Death by 25 Treatment: • Steroid drugs and supplements • Working on gene therapy

  32. X-inactivation • Females have 2 copies of X • One is randomly turned off early in development • Different cells have different Xs active

  33. Chromosomal Disorders • Rather than 1 gene effecting one protein an entire chromosome is deleted or added. • Cause: • Non-disjunction of chromosomes (autosomes or sex chromosomes) during meiosis • Examples: Down Syndrome, Turner’s Klinefelter’s

  34. Nondisjunction Section 14-2 Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II Go to Section:

  35. Nondisjunction Section 14-2 Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II Go to Section:

  36. Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II Section 14-2 Go to Section:

  37. Chromosomal Disorder Down Syndrome • Genotype: (autosomal) 47 XX +21 47 XX +21 • Expression: • Non-disjunction of chromosome 21 • Mental retardation, growth failure, intestinal and heart problems, leukemia, early onset Alzheimer’s • Treatment: • No specific treatment

  38. Incidence of Down’s Syndrome and mother’s age

  39. Chromosomal Disorders • Non disjunction of sex chromosomes leads to extra of loss of an X or Y chromosome

  40. Chromosomal Disorders Turner’s Syndrome Genotype: (sex chromosome) 45 XO Expression: • Female • Sterile • Sex organs do not fully develop during puberty Treatment • Growth hormone treatment, estrogen treatment

  41. Chromosomal Disorders Klinefelter’s Syndrome Genotype: (sex chromosome) 48 XXXY Expression: • Male • Sterile • Breast growth • Language problems • Lower energy Treatment • Testosterone replacement, speech therapy, breast reduction, physical therapy

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