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Text Box: MUTATIONS             A mutation is a permanent change in one or more genes that can be inherited.  Mutations can be caused by: 1)      X-rays 2)      Radiation 3)      Chemicals called ‘mutagens’   Types of Mutations   Chromosomal Mutations: Affect the structure and / or number of chromosomes. (ex. Translocation of part of a chromosome to a different chromosome)   Point Mutations: Affect only one gene             Base Pair substitution (ex. TA replaced by GC)             Frame Shift mutation – caused by the addition or deletion of base pairs from DNA. Everything after that point is effected.    DNA GCA GCA GCA GCA   mRNA CGU CGU CGU CGU   Amino Acid Arg Arg Arg Arg   An addition cause a frame shift DNA GCA TGC AGC AGC A mRNA CGU ACG UCG UCG U Amino Acid Arg Thr Ser Ser     Adding or deleting one base has a greater effect than adding or deleting a codon.   Throughout evolutionary history, mutations that have enhanced survival have been passed on to the next generation.  Mutations that are harmful may cause the organism to die before it can reproduce.    DNA Repair of a Mutated Strand               If only one strand of the DNA molecule has mutated the cell can use the unaffected strand as a template to repair the mutated strand using one of two methods: Before adding the next nucleotide during replication of DNA, the enzyme polymerase is able to proofread its work. Some enzymes are able to ‘cut’ mutations out of DNA.  This must be done before the DNA replicates so that the mutation is not passed down to all succeeding daughter cells.    ONCOGENES AND CANCER   Cancer: Cells dividing out of control (mitosis does not turn off)   Oncogenes: Genes on chromosomes that ‘turn on’ cell division.   Structural Genes: Genes that regulate the synthesis of proteins (ex. Gene that controls hemoglobin)   Regulator Genes:  control the production of repressor proteins which switch off structural genes.  (ex. Regulator genes switch off the structural gene for making hemoglobin in all cells except bone marrow.  Regulator genes switch on the structural gene for making keratin in most cells except skin cells).   Oncogenes leave the ‘switch’ regulating cell division open so cells divide out of control.