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MUTATIONS

MUTATIONS. How mistakes are made…. Mutations. Mutations are defined as “a sudden genetic change in the DNA sequence that affects genetic information”. They can occur at the molecular level (genes) and change a single gene, or at the chromosome level and affect many genes.

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MUTATIONS

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  1. MUTATIONS How mistakes are made…

  2. Mutations • Mutations are defined as “a sudden genetic change in the DNA sequence that affects genetic information”. • They can occur at the molecularlevel (genes) and change a single gene, or at the chromosomelevel and affect many genes.

  3. Things that can cause mutations are called “mutagens”. • Known mutagens are ultraviolet light, cigarette smoking, some viruses, certain chemicals like PCB’s. • Mutagens often result in cancer.

  4. Inheritability of Mutations It depends on where it occurs • Germ mutations – occur in gametes. Inheritable (colorblindness, hemophilia) • Somatic mutations – affect body cell, not inheritable (CAN RESULT IN cancer)

  5. Effects of Mutations Not all mutations have effects. Silent mutations - have no effect on the expression of the gene. • Causes for this type of mutation: • It is in a non-coding region • It does not change the amino acid sequence • The change does not affect the folding of the protein

  6. Types of Mutations • Point Mutations – effects a single gene i. Substitution ii. Frameshift a. deletion b. insertions • Chromosomal Mutations – most drastic, change in structure or # of chromosomes (affects many genes)

  7. Point Mutations • Substitution – one base exchanges for another, affects 1 amino acid(Ex. GCA-TCA  GCT-TCA

  8. The Effects of Point Mutations • A point mutation is a change in a single base pair in DNA. • A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein. Normal mRNA Protein Stop ReplaceG with A Point mutation mRNA Protein Stop

  9. Effects of substitution mutations • Missense mutations – causes a change in the amino acidcoded for • Nonsense mutations – causes a stop codon to occur prematurely

  10. Sickle cell anemia

  11. Tay-Sachs

  12. Frameshift Mutations • What would happen if a single base were lost from a DNA strand? • A mutation in which a single base is added or deleted from DNA is called a frameshift mutation because it shifts the reading of codons by one base. • As a result, everycodonafter the deleted base would be different. Deletion of U mRNA Protein

  13. Frameshift– affects several amino acids -Insertion– 1 base is inserted, affects several amino acids Ex. (GCA-TCA  GCA-GTC-A -Deletion – base is removed, affects several amino acids Ex. (GCA-TCA  GCT-CA

  14. X

  15. Cystic fibrosis

  16. Chromosome mutations Nondisjunction – incomplete chromosome division during meiosis; results in gametes with too many or too few chromosomes. Ex: Down syndrome is caused by an extra #21 chromosome

  17. Aneuploidy Polyploidy

  18. Down’s Syndrome • Trisomy 21 • 1 in 700 births • Mental retardation • Vision problems • Heart problems

  19. Likelihood of chromosomal mutations • 1 in 1700 for mothers under 20. • 1 in 1400 for mothers between 20 and 30. • 1 in 750 for mothers between 30 and 35. • 1 in 16 for mothers over 45.

  20. Sex chromosome disorders – occurs as a result of nondisjunction of the sex chromosomes • Ex: Turner’s syndrome – X-; Klinefelter’s syndrome – XXY.

  21. Klinefelter’s Syndrome • XXY • 1 in 1,000 • Usually sterile because of low sperm count • Tall, sparse body hair • Suffer from gynecomastia- male breast tissue • Testosterone treatments

  22. Turner’s Syndrome • XO genotype—Monosomy X • 1 in 2,500 births • Short, sterile • 75% result in non-disjunction from the father

  23. XYY-Jacob’s Syndrome a.k.a. “Super Males” • 1 in 1,000 men • Normal appearance, very tall • Low IQ, prone to violence

  24. Patau’s Syndrome • 1 out of 6,000 births • Trisomy 13 • 80-90% do not survive past 1 yr old

  25. Trisomy 18 • Second most common trisomy after down’s syndrome • Only 5% live to age 1 • 1 out of 8,000 births • Severely retarded, many die from malformed heart • Polydactyly or syndactyly Edward’s Syndrome

  26. Other Chromosomal Mutations • Affect many different genes • Caused by errors in meiosis or environmental disturbances.

  27. Translocation – occurs when a piece of one chromosome breaks off and attaches to a nonhomologous chromosome • Inversion – occurs when a piece of one chromosome breaks off, flips, and reattaches to the same chromosome

  28. Deletion – occurs when a piece of a chromosome breaks off and is lost • Duplication – occurs when a segment of a chromosome is repeated

  29. Cri du Chat • “Cry of the Cat” • 1 in 50,000 births • A piece of chromosome 5 is missing • Severe mental retardation, nonverbal • Does not run in families

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