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12.4 Mutations

12.4 Mutations. Kinds of Mutations Significance of Mutations. Kinds of Mutations. Sometimes, cells make a mistake in copying their DNA, inserting an incorrect base or even skipping a base as the new strand is put together. Mutations: changes in the genetic material.

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12.4 Mutations

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  1. 12.4 Mutations • Kinds of Mutations • Significance of Mutations

  2. Kinds of Mutations • Sometimes, cells make a mistake in copying their DNA, inserting an incorrect base or even skipping a base as the new strand is put together. • Mutations: changes in the genetic material. • Gene mutations: changes in a single gene. • Chromosomal mutations: changes in a whole chromosomes.

  3. Gene Mutations • Point mutations: gene mutations involving changes in one or a few nucleotides; occur at a single point in the DNA • Substitutions: one base is changed to another; usually only affects one amino acid • Effects of insertions and deletions can be much more dramatic. • If a nucleotide is added or deleted, the bases are still read in groups of three, but now those groupings are shifted • Called frameshift mutations because they shift the reading frame of the DNA • This kind of mutation may change every amino acid after that point. • Can alter a protein so much that it is unable to perform its normal function.

  4. Chromosomal Mutations • Involves changes in the number or structure of chromosomes. • These change the locations of genes on chromosomes. • Deletions: the loss of all or part of a chromosome. • Duplications: extra copies of parts of a chromosome. • Inversion: reverses the direction of parts of chromosomes. • Translocations: occurs when part of one chromosome breaks off and attaches to another.

  5. Significance of Mutations • Most mutations are neutral meaning they have little or no effect on the expression of genes or the function of proteins. • Others have major effects on the expression of genes. • These mutations offer great variability among species some of which may be beneficial. • These mutations may cause some of the disorders we have previously discussed. • Polyploidy: condition in which an organism has extra sets of chromosomes.

  6. Causes of Mutations • Mutations are generally cause by one of two factors. • Either the DNA fails to copy correctly • Environmental factors cause the DNA to mutate

  7. Effects of Mutations • No change in phenotype • Small change in phenotype • Big change in phenotype

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