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DNA Mutations Chapter 12.4 Mutation • Mutation: Any change in a gene is a mutation. • Substances that cause a mutation are called mutagens. • Mutations can also happen spontaneously. Point Mutation • A change in one nucleotide • Original: The fat cat ate the wee rat. Point Mutation: The fat hat ate the wee rat. Point Mutation • Base Substitution - One nucleotide is replaced with another nucleotide. ACC CUA GGC AUC AU ACC UUA GGC AUC AU “C” is substituted with “U” Redundant Systems • Sometimes these mutations have no effect!! Ex. The codons of UCU, UCC, UCA, & UCG all code for the amino acid Serine. Any substitution in the third base of the codon has no effect. • However, a substitution in the first or the second base of the codon, changes the code for the amino acid. • UUU codon is for phenylalanine • UCU codon is for serine • CUU codon is for leucine Frameshift Mutations • Either the insertion or a deletion of a nucleotide which results in a shift in the code and mistakes from the point of mutation on. • Original • Frame Shift The fat cat ate the wee rat. The fat caa tet hew eer at. Somatic Cell mutations • Mutations happen in all organisms, if it happens in a somatic cell then only the individual is affected. Meiosis Mutations • If it happens in a gamete then the mutation is passed on to the offspring. Meiosis Mutations • Mistakes during meiosis: Mistakes during meiosis, such as non-disjunction, can result in three chromosomes instead of a pair (trisomy) or more than three (polyploidy). Down’s Syndrome • Trisomy in humans can result in birth defects such as trisomy 21, or Down’s syndrome. Quick Review • Point mutations occur as a result of a change in one nucleotide. • The 2 basic types of point mutations are base substitutions and frame shift. Quick Review • Substitution mutations are the result of one nucleotide being replaced by another. This results in one amino acid being incorrectly coded. Quick Review • Frame shift mutations are the result of either a deletion or an insertion of a nucleotide. This results in a mistake in all the triplet codes from the mutation on. Gene Mutations • Gene Mutations occur as a result of changes in chromosomal fragments. There are four basic types: • 1. Translocation • 2. Inversion • 3. Insertion • 4. Deletion Gene Mutations 1.Translocations When part of one chromosome breaks off and is added to a different chromosome. Gene Mutations 2. Inversion – When part of a chromosome breaks out and is reinserted backwards. Gene Mutations 3. Insertion When part of a chromatid breaks off and attaches to its sister chromatid. The result is a duplication of genes on the same chromosome. Gene Mutations 4. Deletion When part of a chromosome is left out. Mutations & Evolution • Mutations that have a negative effect usually result in the loss of that mutation due to the law of the survival of the fittest. Mutation & Evolution • However, there are times that the mutations are beneficial and result in the evolution of the species and increased variation in the population. • We’ll learn much more about this next unit!!!