Mutations

Mutations in DNA & RNA

Define mutation

a change in the normal DNA sequence

What are the 2 general categories of mutations?

1. single gene mutations

2. chromosomal mutations

single gene mutations...

changes in nucleotide sequence of one gene

chromosomal mutations…

changes in chromosomes, involve many genes

What are point mutations?

• a change in one nucleotide OR base pair in a gene

• either substitution, insertion, or deletion

• usually occur due to an uncorrected mistake in DNA replication

Insertions can be fixed by…

exonucleases

Can deletions be fixed?

rarely reversible

When is a point mutation not a problem?

if it occurs in an intron section (do not code for protein)

When is a point mutation a problem?

if it occurs in an exon region (do code for protein)

What is a frameshift mutation?

if a # of nucleotides is added or removed that is not a factor of 3 (codon) this causes the entire reading frame of the gene to be altered

Effects of mutations on protein have 3 categories…

1. silent

2. missense

3. nonsense

Define silent mutations

due to the redundancy of genetic code, silent mutations code for the same amino acid

Define missense mutations

the mutations codes for a different amino acid

Define nonsense mutations

this change results in a premature stop codon

Define chromosomal mutations

• any change to chromosome # is always detrimental, if not lethal to the organism

• may also involve the rearrangement of genetic material which can affect several genes & several chromosomes

What are the 4 types of chromosomal mutations?

1. deletions —> loss of genes

2. duplications —> multiple copies of genes or even chromosomes

3. inversions —> reversal of a segment of DNA

4. translocation —> trading of chromosomal segments between 2 different chromosomes (usually not the same size segment being traded)