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Mutations Ch-Ch-Ch-Changes Variation & Speciation Variation also allows sexually reproducing organisms to adapt to a changing environment. The mechanism of mutation in DNA generates variation with natural selection of individuals in populations to produce new species. How Mutation Works Cell DNA Transcription Translation mRNA Ribosome Polypeptide (protein) ©1998 Timothy G. Standish Mutation Mutation = Change Biologists use the term “mutation” when talking about any change in the genetic material. Not all result in a change in phenotype. Macromutations Four major types of Macromutations are recognized: 1 Deletions - Loss of chromosome sections 2 Duplications - Duplication of chromosome sections 3 Inversions - Flipping of parts of chromosomes 4 Translocations - Movement of one part of a chromosome to another part Macromutation - Deletion Chromosome Centromere Genes A B C D E F A B C D G H G H E F Macromutation - Duplication Chromosome Centromere Genes A B C D E F G H A B C D E F EE FF Duplication G H Macromutation - Inversion Chromosome Centromere Genes A B C D E F A B C D F E Inversion G H G H Macromutation - Translocation Chromosome Centromere A B C A B E Genes D F E C F G H D G H Micro or Point Mutations 1 2 Additions - Addition of one or two nucleotides Deletions - Loss of one or two nucleotides Micro Mutations 3’AGTTCAG-TAC-TGA-ACA-CCA-TCA-ACT-GATCATC5’ 5’AGUC-AUG-ACU-UGU-GGU-AGU-UGA-CUAGAAA3’ Met Thr Cys Gly Ser 3’AGTTCAG-TAC-TGA-AAC-CAT-CAA-CTG-ATCATC5’ 5’AGUC-AUG-ACU-UUG-GUA-GUU-GAC-UAG-AAA3’ Met Thr Leu Val Val Val Micro-mutations tend to have a dramatic effect on proteins as all codons down stream from the mutation are changed and thus code for different amino acids. As a result, the length of the polypeptide may also be changed as a stop codon will probably come at a different spot than the original stop codon. Mutations Are Uncommon Cells have many different mechanisms for preventing mutations These mechanisms make mutations very uncommon Even when point mutations occur in the DNA, there may be no change in the protein coded for Mutagens • Mutations often occur naturally as a result of random errors in replication. • Environmental Factors • Radiation - X-ray -Ultraviolet radiation • Chemicals - Mustard gas - Chloroform The Sickle Cell Anemia Mutation Normal b-globin DNA C Mutant b-globin DNA T T C G A A G U A mRNA mRNA Normal b-globin Mutant b-globin Glu H2 N C C A T Val O OH H CH2 H2C C OH O Acid H2 N C C O OH H CH CH3 H3C Neutral Non-polar Sickle Cell Anemia: A Pleiotropic Trait Mutation of base 2 in b globin codon 6 from A to T causing a change in meaning from Glutamate to Valine Mutant b globin is produced Breakdown of Red blood cells Anemia Clogging of small Blood vessels Tower skull Weakness Heart failure Impaired mental function Accumulation of sickled Cells in the spleen Red blood cells sickle Brain damage Paralysis Pain and Fever Damage to other organs Rheumatism Kidney failure Infections Especially Pneumonia Spleen damage