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Transcript
Chapter 11 DNA and Genes Section 3 Genetic Changes Mutations A mutation is any change in the DNA sequence. Mutations can be caused by: Errors in: replication. transcription. cell division. External agents. Mutations in Reproductive Cells The mutation occurs in the gamete and is passed on to the zygote. May be beneficial or harmful: May result in a new trait which benefits the organism or in structural or functional problems in the cells or the organism. At times, the problem is so severe that the organism does not survive. Mutations in Body Cells DNA is changed by an outside force (such as radiation). This change may impair the function of the cell. The mutation is passed on to daughter cells when the original cell divides. Example: Cancer Point Mutation A change in a single base pair in DNA. Can change the coding for amino acids, which can result in a different protein. Frameshift Mutation Results when a single base is missing or is added in DNA and is then transcribed into mRNA. Changes nearly every amino acid located after the deletion or addition in the protein. Chromosomal Mutations Can occur in a variety of manners: Parts of the chromosome can be broken off and lost during mitosis or meiosis. The chromosome can break and rejoin incorrectly (backward or to the wrong sections). Chromosomal Mutations Very common in plants. During meiosis the homologous chromosomes will not pair correctly when one chromosome has extra or missing parts, resulting in incorrect separation of the homologous chromosomes, leaving one gamete with too many chromosomes and the other with not enough. Chromosomal Mutations Few chromosomal mutations are passed on to the next generation because the zygote usually does not survive. In cases that the organism reaches maturity, it is usually sterile. Causes of Mutations May be spontaneous Simply occur. Caused by mutagens Any agent that can cause a change in DNA. Examples: radiation (X-rays, UV rays, nuclear radiation), chemicals (dioxins, asbestos, benzene, formaldehyde), and high temperatures. Greater the exposure is to mutagens the more likely it is that mutations will form. Repairing DNA Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides.
