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MUTATIONS SC STANDARD B-4.9: The student will exemplify ways in which new characteristics are introduced into an organism or a population Cornell Notes Page 110 Topic: Mutations Essential Question: What is a mutation, how do mutations allow a species to change over time? Mutation: The Basis of Genetic Change A mutation is a change in the structure or amount of genetic material of an organism In general, genetic differences among organisms originated as some kind of genetic mutation. Causes of Mutations Occur naturally as accidental changes in DNA or chromosomes repair enzymes “overlook” errors Rate of mutation can be accelerated by some environmental factors called mutagens forms of radiation chemicals Effects of Mutations Depends on where and when mutations occur Germ Cell mutations passed on to offspring Somatic Cell Mutations not passed on to offspring could result in • Normal tissue • Cancer Kind of Mutations 1. Mutations as changes in DNA 1. Point Mutation 1. change of a single nucleotide from 1 base to another 2. Insertion or Deletion 1. single nucleotide in a sequence added or dropped 1. rare Point Mutation Insertion or Deletion Mutations as Changes in Results of Genes 1. Silent Mutations 1. has no effect on gene’s function 2. frequently happens because genetic code is redundant Mutations as Changes in Results of Genes 2. Missense or Replacement Mutations codon changed so results in a different amino acid Mutations as Changes in Results of Genes 3. Frameshift Mutations “reading frame” of a codon depends on the starting point insertions or deletions may shift the reading frame which may cause the remaining sequence of nucleotides to be “read” as different codons Frameshift Mutations Mutations as Changes in Results of Genes 4. Nonsense Mutation results when a codon is changed from an amino acid to a “stop” signal - resulting protein will be cut short & may fail to function Nonsense Mutation Mutations 5. More or Fewer Amino Acids if an insertion or deletion is a multiple of 3 the resulting protein will have fewer or more amino acids the more codons that are inserted or deleted the more likely the resulting protein will be malfunctioning Chromosomal Mutations In eukaryotic cells, the process of meiosis creates the chance of mutations at the chromosomal level: involve changing the location of genes on chromosomes, or the numbers of copies of some genes 4 Types of Chromosomal Mutations 1. Deletions 2. Duplications Involve loss of all or a Produce extra copies part of a of parts of a chromosome chromosome 3. Inversions Reverse the direction of parts of chromosomes 4. Translocations Occur when a part of one chromosome breaks off & reattaches on the end of another chromosome Trisomies 3 copies of a chromosome, in whole or in part seen in several different chromosomes most commonly in chromosome 21 Karyotype of Trisomy 21 Significance of Mutations 1. Neutral 1. most mutations 2. Lethal or Harmful 1. resulting proteins defective, disrupt normal activity 3. Beneficial 1. new altered protein offers individual advantages Somatic cell mutations: affect individual only Germ Cell mutations passed on to offspring Basis for new genetic variation in population Polyploidy condition in which organism has extra sets of chromosomes (due to failure in meiosis) Polyploidy plants often hardier, larger than diploid plants Animations http://highered.mheducation.com/sites/007 2556781/student_view0/chapter11/animati on http://www.dnatube.com/video/685/DNA-Duplication-and-Mutations