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DNA Mutations. Chapter 12.4. Mutation. Mutation : Any change in a gene is a mutation. Substances that cause a mutation are called mutagens. Mutations can also happen spontaneously. Point Mutation. A change in one nucleotide

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DNA Mutations

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DNA Mutations

Chapter 12.4


  • Mutation: Any change in a gene is a mutation.

  • Substances that cause a mutation are called mutagens.

  • Mutations can also happen spontaneously.

Point Mutation

  • A change in one nucleotide

  • Original: The fat cat ate the wee rat. Point Mutation: The fat hat ate the wee rat.

Point Mutation

  • Base Substitution - One nucleotide is replaced with another nucleotide.


    “C” is substituted with “U”

Redundant Systems

  • Sometimes these mutations have no effect!! Ex. The codons of UCU, UCC, UCA, & UCG all code for the amino acid Serine. Any substitution in the third base of the codon has no effect.

  • However, a substitution in the first or the second base of the codon, changes the code for the amino acid.

  • UUU codon is for phenylalanine

  • UCU codon is for serine

  • CUU codon is for leucine

Frameshift Mutations

  • Either the insertion or a deletion of a nucleotide which results in a shift in the code and mistakes from the point of mutation on.

  • Original The fat cat ate the wee rat.

  • Frame ShiftThe fat caa tet hew eer at.

Somatic Cell mutations

  • Mutations happen in all organisms, if it happens in a somatic cell then only the individual is affected.

Meiosis Mutations

  • If it happens in a gamete then the mutation is passed on to the offspring.

Meiosis Mutations

  • Mistakes during meiosis: Mistakes during meiosis, such as non-disjunction, can result in three chromosomes instead of a pair (trisomy) or more than three (polyploidy).

Down’s Syndrome

  • Trisomy in humans can result in birth defects such as trisomy 21, or Down’s syndrome.

Quick Review

  • Point mutations occur as a result of a change in one nucleotide.

  • The 2 basic types of point mutations are base substitutions and frame shift.

Quick Review

  • Substitution mutations are the result of one nucleotide being replaced by another. This results in one amino acid being incorrectly coded.

Quick Review

  • Frame shift mutations are the result of either a deletion or an insertion of a nucleotide. This results in a mistake in all the triplet codes from the mutation on.

Gene Mutations

  • Gene Mutations occur as a result of changes in chromosomal fragments. There are four basic types:

  • 1. Translocation

  • 2. Inversion

  • 3. Insertion

  • 4. Deletion

Gene Mutations

1.Translocations - When part of one chromosome breaks off and is added to a different chromosome.

Gene Mutations

2. Inversion – When part of a chromosome breaks out and is reinserted backwards.

Gene Mutations

3. Insertion When part of a chromatid breaks off and attaches to its sister chromatid. The result is a duplication of genes on the same chromosome.

Gene Mutations

4. Deletion

When part of a chromosome is left out.

Mutations & Evolution

  • Mutations that have a negative effect usually result in the loss of that mutation due to the law of the survival of the fittest.

Mutation & Evolution

  • However, there are times that the mutations are beneficial and result in the evolution of the species and increased variation in the population.

  • We’ll learn much more about this next unit!!!

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