Topic 8 - Control of gene expression Flashcards
define gene mutation
a change in the sequence of bases in a DNA molecule that may result in an altered polypeptide
how can mutations occur
spontaneously and continously
when do mutations usually occur
interphase - DNA replication
why do most mutations have little or no effect
due to degeneracy of genetic code
how can mutations arise from
nucleotide changes: insertion, deletion, substitution
structural changes: inversion, duplication, translocation
give 2 examples of mutagenic agents
- high energy ionising radiation such as alpha/beta/gamma radiation
- chemicals such as NO2 from tobacco smoke
what three forms can substitution mutations take
silent, nonsense, missense
define silent mutation
no change to the amino acid sequence due to the degeneracy of the genetic code
define missense mutations
alters a single amino acid potentially affecting protein function
give an example of missense mutation
sickle cell anemia
define nonsense mutations
creates a premature stop codon, producing an incomplete non-functional protein
give an example of nonsense mutation
cystic fibrosis
when does inversion mutations usually occur
during crossing over in meiosis
what happens in inversion mutations
DNA of a single gene is cut into two places. the cut portion is inverted 180 then rejoined to the same place
results in a large section of gene is backwards and multiple amino acids are affected as they are being read incorrectly
what usually results in inversion mutations
non-functional protein, or in some cases a completely new protein
