Mutations

Good or Bad?

• Good - the change in the DNA sequence may lead to a positive effect for the organism

• Bad - negative effect on the organism

• Benign - no effect (introns, wobble position, after termination sequence, in a telomere, non-coding regions : promoters, regulatory sequence, in a silenced or non-expressed gene) → Protein level is not affected

Point Mutations

A change in a single nucleotide

• Substitution Mutation - Replacement of a single nucleotide ; may change one amino acid it codes for

• Frame Shift Mutation - An addition of a nucleotide ; will change the coding along the whole sequence → Shift the “reading frame” of the ribosome → more harmful

Point Mutation : Silent

• May occur in the introns (non-coding) of the DNA

• May be due to the redundant nature of DNA (Multiple copies of same gene)

• May be a change in the wobble position where the codon still codes for the same amino acid

Point Mutation : Missense

• Base (Nucleotide) change alters the codon leading to a different amino acid

• Ex : Sickle Cell Anemia

Point Mutation : Nonsense

• Nucleotide gets changed and causes a codon to become a stop codon

• Stop codon in the middle of a gene is often lethal to the cell

• Changes the ‘class’ of an amino acid

Point Mutation : Insertion or Deletion

• A nucleotide is added or deleted

• Every codon after the frame shift is different

• Leads to a non-functioning protein

• Multiples of 1 or 2 are the worst

Conservative and Non-Conservative

• If an amino acid changes, but it’s class of polarity remains the same (Polar→ Polar / Non-Polar → Non-Polar) it is a conservative mutation and has the same properties

• If an amino acid changes, and it’s class of polarity changes (Polar → Non-Polar / Polar → Electrically Charged) it is a non-conservative mutation and has different properties

Chromosomal Mutation

Not just errors in meiosis where a whole extra chromosome or missing a chromosome

• Can involve a rearrangement of genetic material

• Changes to chromosome structure can include deletions, duplication, inversion or translocation of portions to the chromosome

• Basically changes that are noticeable in a karyotype

Chromosomal Mutation : Deletion

• Missing a piece of a chromosome

Chromosomal Mutation : Duplication

• Piece of chromosome is copied

• Organisms is unaffected → can provide long term benefits to species

• Important in evolution → Extra copy is free to mutate and take on extra functions that can be passed on

Chromosomal Mutation : Inversion

• A chromosome segment reverses its orientation in the chromosome

• May disrupt the gene function by impacting promoter region

Chromosomal Mutation : Translocation

• A segment of one chromosome breaks off and changes places with another chromosome segment

• Can result in faulty proteins due to connection issues

Chromosome mutations more serious than point mutations?

Many more genes / proteins are impacted by chromosomal mutations, compared to the singular of point mutations

Causes of Mutations

Spontaneous Mutations : 

• Take place naturally in the cell

• Can be caused by an error in DNA replication

• Transposons (Jumping Genes) segments of DNA that are capable of moving

Induced Mutations : 

• Caused by outside agents

• X-Rays, Chemicals, UV Radiation