Mutation

Mutation

A change in the nucleotide sequence of DNA that is heritable
People like some of the phenotypes produced by mutant alleles
Recessive Mutations
1. Phenotype is associated with the homozygous condition
2. Often involve the loss of gene function
  1. Null / Amorphic Alleles
    1. A nonfunctional protein is produced OR no protein is produced
  2. Hypomorphic Alleles
    1. A poorly functioning protein is produced OR reduced amounts of a normally functioning protein is produced
Dominant Mutations
1. Only need one copy of allele to see phenotype
2. Often involve gain/change of gene function
  1. Dominant Hypermorphic Alleles
    1. Negative phenotypic consequences due to the over-production of a normal protein OR negative phenotypic consequences due to the production of a protein with increased activity levels
  2. Neomorphic Alleles
    1. Negative phenotypic consequences due to the presence of an altered protein that has a new function
Silent Mutation: DNA change results in a new mRNA codon that specifies the same amino acid
Missense Mutation: DNA change results in a new mRNA codon that specifies a different amino acid
Nonsense Mutation: DNA change results in a new mRNA codon that is a STOP codon
Frameshift Mutation: DNA change that results in a change in the reading frame. Downstream from the insertion/deletion, the reading frame is shifted, which results in a very different amino acid sequence for the latter part of the protein
Sources of Mutations
1. Spontaneous: Changes in the nucleotide sequence as a result of errors in the DNA replication
2. Induced: Changes in the nucleotide sequence which result from exposure to radiation and mutagenic chemicals
Certain chemicals are mutagenic

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