Zoo 317 Heredity, Evolution and Society

Lecture 21 Cummings 11: pp 266-282
POINT MUTATIONS

I. The nature of mutations.

II. Mutation rates.

III. Molecular consequences of mutations.

IV. Unstable genes.

Terms.

Erratum
Page 276, margin: The definition of frameshift mutation should read, "Mutational events in which one to two bases are added to or removed from DNA, causing a shift in the codon reading frame."

I. A mutation can be defined as any heritable change.

II. The mutation rate is a measure of the frequency of a given mutation per generation (or per gamete, which is equivalent). Ordinarily, rates are given for specific loci. Thus the mutation rate for achondroplasia is 6-13 mutants per million gametes. This means that each gamete has ca. 1 chance in 100,000 of carrying a new mutation for achondroplasia.

III. The effects of small DNA changes depend on the region of the gene involved.

IV. Some genes and DNA sequences are highly unstable compared to the vast majority of DNA regions. This occurs because of trinucleotide expansion.

[Skip imprinting, which was covered earlier.]


Terms
mutation point mutation germinal mutation
somatic mutation Lesch-Nyhan syndrome mutation rate
nucleotide substitution   synonymous/silent mutation   missense mutation
nonsense mutation sense mutation insertion
deletion frameshift mutation   compound heterozygote  
  trinucleotide expansion   premutation anticipation

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last revision: 28 September 1999
owned by: Dr. Eldon Sutton