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Understanding Genetic Mutations: Point and Frameshift Mutations Explained

Discover how mutations affecting nucleotide sequences lead to different amino acids expression. Learn about point mutations (substitutions, insertions, deletions) and chromosome structure changes (deletion, duplication, inversion, translocation).

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Understanding Genetic Mutations: Point and Frameshift Mutations Explained

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Presentation Transcript

  1. Mutations

  2. Sequence • We have seen that the order of nucleotides dictates the amino acid expressed • If a single base pair is changed in the genetic code, a different amino acid can result • This is called a point mutation • There are two types: substitutions and insertions or deletions

  3. Substitutions • A nucleotide and its complement get replaced by another pair • Often this is a silent mutation – occurs on an intron, or does not change amino acid expressed • For example, if coding strand is changed from CGC to CGT, mRNA changes from CGC to CGU • Both codons yield an arginine

  4. If the mutation does change the amino acid, it is usually a missense mutation • Makes sense, but not the right sense • One of the most commonly cited examples of this is sickle-cell disease

  5. In rare cases, it can change to a stop codon, leading to a premature termination of the protein • This is a nonsense mutation

  6. Insertions and Deletions • Involves addition or loss of one or more nucleotides • Called a frameshift mutation • Can be more of an issue than substitutions as is changes the reading frame • Consider the sentence: “THE CAT ATE THE RAT” • Delete “A” of CAT: • THE CTA TET HER AT

  7. Chromosome Structure • It is also possible to change entire segments of a chromosome • There are four types: deletion, duplication, inversion, and translocation

  8. Deletion • Fragment of chromosome lost during replication

  9. Duplication • When the piece broken off in a deletion reattaches to a homologous chromosome

  10. Inversion • When the fragment reattaches to original chromosome, but has “flipped”

  11. Translocation • Segment reattaches to a nonhomologous chromosome

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