AP Biology Mutations Unit 5B.5

AP Biology 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

AP Biology 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

AP Biology 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

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

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

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

AP Biology 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

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

Sickle cell anemia Slide from Explore Biology by Kim Foglia

AP Biology 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.)

AP Biology

Evidence Distribution of sickle cell trait Distribution of malaria

AP Biology 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.