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Understanding Mutations: Types, Causes, and Effects on Organisms

Mutations are changes in an organism's DNA that can occur in single genes or entire chromosomes. They can alter physical characteristics (phenotype), with some leading to significant changes like sickle cell disease caused by a single amino acid replacement. Mutations can be point mutations (nucleotide substitutions) or frame shift mutations (insertions/deletions). Only germ cell mutations are passed to future generations, while somatic mutations affect only the individual. Environmental agents, or mutagens, can also cause DNA changes. Not all mutations are harmful; some are silent or neutral.

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Understanding Mutations: Types, Causes, and Effects on Organisms

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  1. Mutations

  2. Mutations • Defined: any change in an organism’s DNA • Where: Single genes or entire chromosomes • Some gene mutations change phenotype (physical characteristics) • Example: Can cause a premature stop codon • Some gene mutations don’t change phenotype. • Example: Could be silent or occur in a non-coding region • When: Throughout the life of the cell

  3. Defined: one nucleotide is substituted for another Often repaired by spellchecker enzyme May lead to amino acid change See animation May not lead to any change (Silent Mutation) Ex: DNA “CCC” is mutated into “CCG” Same amino acid is created (glycine) Gene: Point Mutations T A C A G T G G T C A A A DNA U G U C A C A C A G U U U mRNA cysteine glutamine histidine glutamine phenylalanine Amino acids

  4. Point Mutation and Sickle Cell Disease • Hemoglobin (protein) is made from 574 amino acids • Sickle cell disease is caused because of 1 wrong amino acid

  5. Gene: Frame Shift Mutation C A C A G T T G T C A A A DNA • Defined: insertion/deletion of a nucleotide • Entire sequence of DNA/RNA after the mutation is shifted (see animation) • Much more serious to the structure/function of the final protein • mRNA sequence may have an early or late “stop codon” G U G U C A A C A G U U U mRNA cysteine glutamine glutamine phenylalanine Amino acids histidine serine leucine

  6. Gene: Frame Shift Mutation C A C A G T G G T C A A A DNA U G U C A C C A G U U U G mRNA histidine glutamine phenylalanine cysteine Amino acids glutamine proline valine

  7. Impact on Offspring • Somatic cell mutations • Affect only the individual • Not passed on to future generations • Ex: Muscle cell mutation • Germ cell mutations • Germ cells = the diploid cells that undergo meiosis to make sperm & egg • May be passed to future generations If the mutated sperm above were to fertilize this egg…

  8. Mutation Causes • Mutagen: agents in the environment that can change DNA • Speed up replication process • Break apart nucleotides • Ex: UV from sunlight breaks hydrogen bond between thymine (T) and adenine (A)

  9. Review • How are proteins affected if the DNA code is mutated? Example: ATTCGAGG is mutated to ATTCGTGG • What is the difference between a point mutation and frame shift mutations? • When are mutations passed on to future generations? • What are germs cells? • What is a mutagen and how do they cause problems? • Are all mutations considered bad/dangerous? Explain.

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