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Human Genetics

Human Genetics. Section 13.3: Mutations Section 14.1: Human Chromosomes Section 14.2: Human Genetic Disorders. Mutations. Section 13.3. Vocabulary. Mutation Germ Mutation Somatic Mutation Gene Mutation Chromosomal Mutation Point Mutation Frameshift Mutation. Deletion Duplication

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Human Genetics

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  1. Human Genetics Section 13.3: Mutations Section 14.1: Human Chromosomes Section 14.2: Human Genetic Disorders

  2. Mutations Section 13.3

  3. Vocabulary • Mutation • Germ Mutation • Somatic Mutation • Gene Mutation • Chromosomal Mutation • Point Mutation • Frameshift Mutation • Deletion • Duplication • Inversion • Translocation • Nondisjunction • Monosmy • Trisomy • Polyploidy

  4. Types of Mutations • Mutations are heritable changes in genetic information. • A mutation results from a mistake in duplicating genetic information (DNA replication).

  5. Types of Cells Affected • Germ Mutation - affects a reproductive cell (gamete or sperm/egg) • Does not affect the organism • Passed to offspring • Somatic Mutation – affects body cells (all cells except gametes) • Not passed to offspring

  6. Types of Mutations • All mutations fall into two basic categories: • Those that produce changes in a single gene are known as gene mutations. • Those that produce changes in a part of a chromosome, whole chromosomes, or sets of chromosomes are known as chromosomal mutations. Ameoba Sisters – Mutations(7 min)

  7. Mutagens • Mutations can be caused by chemical or physical agents (mutagens) • Chemical – pesticides, tobacco smoke, environmental pollutants • Physical – X-rays and ultraviolet light

  8. Gene Mutations • Mutations that involve changes in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence. They generally occur during replication. • If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one.

  9. Gene Mutations • Point mutations include substitutions, insertions, and deletions.

  10. Substitutions • In a substitution, one base is changed to a different base. • Substitutions usually affect no more than a single amino acid, and sometimes they have no effect at all.

  11. Substitution - Silent Mutation • a change in one base pair has no effect on the protein produced by the gene. • This is allowed for by the redundancy in the genetic code. • Example (as shown in picture): • Both GGC and GGU code for the amino acid glycine. • Thus, the mutation is “silent,” i.e. causes no change in the final protein product.

  12. Substitution - Missense Mutation • a change in one base pair causes a single amino acid to be changed in the resulting protein. • The result is called “missense” since the code is now different. • In the following example, GGC has been changed to AGC, resulting in a different amino acid.

  13. Substitutions - Missense • In this example, the base cytosine is replaced by the base thymine, resulting in a change in the mRNA codon from CGU (arginine) to CAU (histidine).

  14. Sickle Cell Anemia • The effect of a missense mutation on the protein is unpredictable. • A missense mutation is the cause of the disease, sickle cell anemia. • a change in one base pair alters one amino acid • effects hemoglobin protein, causing red blood cells to take on a strange shape

  15. Sickle Cell Anemia

  16. Substitution - Nonsense Mutation • a change in a single base pair creates a stop codon. • Because this kind of mutation creates a stop signal in the middle of a normally functional gene, the resulting protein is almost always nonfunctional • hence the term “nonsense” mutation.

  17. Substitution Silent Mutation Missense Mutation Nonsense Mutation

  18. Insertions and Deletions • Insertions and deletions are point mutations in which one base is inserted or removed from the DNA sequence. • If a nucleotide is added or deleted, the bases are still read in groups of three, but now those groupings shift in every codon that follows the mutation.

  19. Frameshift Mutation • Insertions and deletions are also called frameshift mutations because they shift the “reading frame” of the genetic message. • Frameshift mutations can change every amino acid that follows the point of the mutation and can alter a protein so much that it is unable to perform its normal functions.

  20. Frameshift Mutation: • Example: • Deletion: • THE FAT CAT ATE THE RAT • THE FAT ATA TET HER AT • Insertion: • THE FAT CAT ATE THE RAT • THE FAT CAR TAT ETH ERA T

  21. Insertions

  22. Deletions

  23. Gene Mutations:

  24. Chromosomal Mutations • Chromosomal mutations involve changes in the number or structure of chromosomes. • These mutations can change the location of genes on chromosomes and can even change the number of copies of some genes.

  25. Chromosomal Mutations • Deletion involves the loss of all or part of a chromosome.

  26. Chromosomal Deletion • Example: Cri-du-chat (5p minus) – a piece of chromosome 5

  27. Cri du chat • intellectual disability/delayed development • small head size (microcephaly), • low birth weight • weak muscle tone (hypotonia) in infancy • widely set eyes (hypertelorism) • low-set ears • a small jaw • a rounded face • heart defect

  28. Chromosomal Mutations • Duplication produces an extra copy of all or part of a chromosome.

  29. Chromosomal Duplication

  30. Fragile X - Most people have 29 "repeats" at this end of their X-chromosome, those with Fragile X have over 700 repeats due to duplications

  31. Fruit flies experience a change in eye size of when duplication occurs.

  32. Chromosomal Mutations • Inversion reverses the direction of parts of a chromosome.

  33. Chromosomal Inversion

  34. Chromosomal Mutations • Translocation occurs when part of one chromosome breaks off and attaches to another. Example: acute meyloid leukemia

  35. Chromosomal Translocation

  36. Inversions

  37. Nondisjunction • Chromosomal mutations that involve whole chromosomes or complete sets of chromosomes results from a process known as nondisjunction • This is the failure of homologous chromosomes to separate normally during meiosis.

  38. Nondisjunction

  39. Nondisjunction

  40. Nondisjunction

  41. Effects of Nondisjunction • If one chromosome is involved, the condition of one extra is called trisomy or one less is monosomy

  42. Trisomy 21

  43. Patau Syndrome (trisomy 13) - serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months

  44. Edward’s Syndrome (trisomy 18) - almost every organ system affected 1:10,000 live births. Children generally do not live more than a few months

  45. Trisomy X (XXX) • females. 1:1000 live births - healthy and fertile - usually cannot be distinguished from normal female except by karyotype

  46. Monosomy X aka Turner Syndrome • the only viable monosomy in humans • only 45 chromosomes • genetically female, however, they do not mature sexually during puberty and are sterile. • Short stature and normal intelligence • 98% of these fetuses die before birth

  47. Klinefelter Syndrome (XXY) • Affects male sex organs (small testes, sterile). • feminine body characteristics. • Normal intelligence.

  48. Nondisjunction • If nondisjunction involves a set of chromosomes: • The condition in which an organism has extra sets of chromosomes is called polyploidy. • Triploid (3n) • Tetraploid (4n) • Polyploid (many sets)

  49. Beneficial Effects • Plant and animal breeders often make use of “good” mutations. • For example, when a complete set of chromosomes fails to separate during meiosis, the gametes that result may produce triploid (3N) or tetraploid (4N) organisms.

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