BIOL 1090 Lecture Notes - Lecture 10: Cytosine, Chromosome Abnormality, Pyrimidine Dimer

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Mutation is the source of all genetic variation. Insertion of a transposable element into a gene. Mutations occur in all organisms from viruses to humans. During meiosis, crossing over rearranges genetic variability into new gene combinations. Natural selection preserves the combinations best adapted to the existing environment. Germinal mutations occur in germ-line cells and will be transmitted through the gametes to the progeny. Somatic mutations occur in somatic cells; the mutant phenotype will occur only in the descendants of that cell and will not be transmitted to the progeny. Spontaneous mutations occur without a known cause due to inherent metabolic errors or unknown agents in the environment. Induced mutations result from exposure of organisms to mutagens: physical and chemical agents that cause changes in dna, such as ionizing irradiation, ultraviolet light, or certain chemical. Transition replaces a pyrimidine with another pyrimidine or a purine for another purine. Transversion replaces a pyrimidine with a purine or a purine with a pyrimidine.

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