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Mutations

Mutations. Unit 5B.5. Changes in genotype (DNA) can result in changes in phenotype Alterations in DNA sequence can lead to changes in the type or amount of protein produced and the consequent phenotype. Mutation. Any change in the DNA sequence

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Mutations

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  1. Mutations Unit 5B.5

  2. Changes in genotype (DNA) can result in changes in phenotype • Alterations in DNA sequence can lead to changes in the type or amount of protein produced and the consequent phenotype

  3. Mutation • Any change in the DNA sequence • Can be positive, negative, or neutral based on the effect or the lack of effect the mutation has on the resulting nucleic acid or protein and the phenotype determined by that protein

  4. Causes of Mutations • Errors in DNA replication or DNA repair mechanisms • Wrong base pairing (that doesn’t get caught during proofreading of DNA) • External factors • Radiation • Reactive chemicals • Whether or not the mutation is detrimental, beneficial or neutral depends on the environmental context

  5. 1st to suggest genes dictate phenotypes through enzymes that catalyze specific chemical reactions • Postulated that the symptoms of an inherited disease are due to inability to make a specific enzyme • Coined term “inborn errors of metabolism” to describe such diseases • Beginning of “One gene-one enzyme” hypothesis • ALCAPTONURIA- “black urine” disease- defect in enzyme that breaks down amino acid tyrosine ARCHIBALD GARROD 1902 http://www.personal.psu.edu/faculty/w/x/wxm15/Online/Molecular%20Biology/media/phenylalanine.gifhttp://www.nature.com/bjp/journal/v147/n1s/images/0706466f5.jpg

  6. Mutations • Point mutations • single base change • base-pair substitution • silent mutation • no amino acid change • redundancy in code • missense • change amino acid • nonsense • change to stop codon Slide from Explore Biology by Kim Foglia

  7. Mutations • Frameshift • shift in the reading frame • changes everything “downstream” • insertions • adding base(s) • deletions • losing base(s) • More damaging atbeginning of gene than at end Slide modified from: Explore Biology by Kim Foglia

  8. Mutations are the primary source of genetic variation in a population • Changes in genotype may affect phenotypes that are subject to natural selection (survival of the fittest) • Genetic changes that enhance survival and reproduction can be selected by environmental conditions • Antibiotic resistance in bacteria • Pesticide resistance • Sickle cell anemia

  9. Point mutation leads to Sickle cell anemia What kind of mutation? Slide from Explore Biology by Kim Foglia

  10. Sickle cell anemia Slide from Explore Biology by Kim Foglia

  11. Heterozygotes have both normal and sickle cells. • These people are normal and healthy. • Individuals that have sickle cell anemia (homozygous for the trait) will have slow blood and the blood cells have a shorter life span than normal cells (these people tend to get sicker more frequently and can have serious health problems.)

  12. Evidence Distribution of malaria Distribution of sickle cell trait

  13. As is the case with sickle cell anemia, a heterozygote may be a more advantageous genotype than a homozygote under particular conditions, since with different alleles, the organism has two forms of proteins that may provide functional resilience in response to environmental stresses.

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