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bis 101
engebrecht
14
Biology
Undergraduate 1
06/12/2007

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Term
Transitions
Definition
Base changes from one purine (A/G) to another purine.

Or one pyrimidine (C/T) to another pyrimidine
Term
Transversions
Definition
Base changes from a purine (A/G) to a pyrimidine (C/T)

or vice versa
Term
Silent Mutations
Definition
Base change in the open reading frame of a protein coding gene that does not lead to a change in the amino acid sequence. These are often (but not always) in the 3rd codon position because of the degeneracy of the genetic code

EX: TTT->TTC both encode phenylalanine
Term
Neutral Mutations
Definition
Base change in the open reading frame of a protein coding gene that leads to a change in the amino acid sequence that does not affect function of protein. Therefore, if there is no phenotype, the mutation is said to be neutral.

EX: AAA->AGA, changes a lysine to an arginine. These are both basic amino acids and in a lot of proteins this change will have no functional consequences (but this is not always the case!)
Term
Missense Mutation
Definition
Base change that leads to an amino acid change in the encoded protein which affects function of the protein. Therefore, there is a phenotype.

EX: AAA-> AAT changes a lysine to an asparagine. This is a change from a basic amino acid to a polar amino acid. Depending on the position this may result in a change in the functioning of the protein
Term
Nonsense Mutation
Definition
Base change that leads to a stop codon

EX: TAC-> TAA changes a tyrosine residue to a stop codon. This will result in a truncated protein and therefore, will most likely be nonfunctional.
Term
Frameshift Mutation
Definition
Addition or subtraction of one or a few bases (but not a multiple of 3), that completely scrambles the genetic code downstream of the mutation. Most likely this will result in a nonfunctional protein
Term
Null Mutation
Definition
Total loss of function, either no gene product is made or the product is nonfunctional. These are usually recessive, unless it is haplo-insufficiency (cant survive with only one copy)

EX: Knockouts because these remove the whole open reading frame. However, a single missense mutation can have the same affect if it changes a critical amino acid for function
Term
Leaky or Hypomorphic Mutation
Definition
A mutation that results in a protein product that is partially functionl

EX: Mutations of the white gene in Drosophila that result in different amount of red pigments
Term
Gain of Function Mutation
Definition
Mutation that confers a new property onto the protein. These are usually dominant mutations

EX: tRNA nonsense suppressor
Term
Conditional Alleles
Definition
A mutation that results in a protein that functions under one environmental condition but not under another

EX: temperature sensitive mutations, at the permissive temperature the protein functions, at the temperatire the protein if nonfunctional
Term
Reversion
Definition
The exact reversal of the initial mutation
Term
Intragenic Suppression
Definition
A compensatory mutation in the same gene, that leads to a wild-type phenotype, although the gene contains two mutations

EX: Original mutation is a +1 frameshift an intragenic suppressor is an adjacent -1 frameshift
Term
Extragenic Suppression
Definition
A mutation in a second gene, that suppresses the mutation in the first gene.

EX: Original mutation is a nonsense mutation, a secondary mutation in the anticodon portion of a tRNA can suppress the mutation
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