Change in the nucleic sequence caused by the addition, removal or rearrangement of one or more nucleotides
Name the types of point mutation and their effect
Silent - no change in the amino acid translated
Missence - Substitution of a base resulting in a replacement of one amino acid for another
Non-sense - substitution of a base changing the amino acid specified to a stop codon
Frameshift mutation - Addition or subtraction of nucleotides not in multiples of 3
What is the cause of a frameshift mutation?
Addition or deletions of bases not in multiples of three
Why can a silent mutations still have serious consequences?
Substitution of a base may occur in a binding site, promoter sequence or splice site on DNA
Explain two ways that spontaneous mutations can occur?
Tautomeric shift - nucleotides briefly change to tautomeric form and so behave as altered template bases in replication
DNA strand slippage - template or new strand loops out during replication causing imperfect base pairing
Name two chemicals that can induce mutation
Nitrous acid, Ethyl methane sulphonate (EMS), IQ
Name two sources of radiation that can induce mutation
X-rays, radon gas in the environment
Why is some ultraviolet B required by humans at healthy levels?
Needed to induce vitamin D production in the skin Too much UVB exposure can cause sun burn and some forms of skin cancer
Name the mechanisms of DNA repair
1) Excision repair - nucleotide excision for UV damage, base excision for oxidative damage
2) Nucleotide mismatch repair - proof reading
3) p53 - monitors and promotes apoptosis when sever damage occurs
What are the mechanisms by which cancer genes become homozygous in order for tumour formation to be initiated?
1) Loss of chromosome with wild type allele
2) Deletion of wild type allele on chromosome
3) Point mutation on chromosome which originally held wild type allele
4) Mitotic Recombination- rare
Name two disease that can be identified by genetic tests and the tests used
Sickle cell anaemia- Southern blotting
Cystic fibrosis- PCR and southern blotting/DNA sequencing
Base substitutions can either be _______ or ______
Transition or transversion
What is a transition point mutation?
Purine substituted with a purine OR pyramidine substituted with pyramidine
What is a transversion point mutation?
purine to pyramidine or vice versa
What is an oncogene?
Genes normally involved in control of cell growth (proto-oncogenes) but has transformed a cell into a tumour cell (oncogenes)