1. Mutations changes in the DNA sequence that can be inherited
can have negative effects (a faulty gene for a trans-membrane protein leads to cystic fibrosis), but most mutations go unnoticed (we have two copies of each gene).
Type 1: Point Mutations
Silent Mutations - have no effect on cell function (two types)
Errors that are located in intron regions - get cut out before translation.
Genetic code redundancy - a change in the sequence may not alter the amino acid (eg. UUU and UUC both result in phenylalanine)
Missense Mutation
When a change in the sequence of DNA alters a codon, resulting in a different amino acid being put in the peptide sequence.
Sickle cell anemia occurs because of a missense mutation.
Nonsense Mutation
A change in the DNA sequence causes a STOP codon to be inserted in place of an amino acid codon.
The protein produced is truncated (too short).
Frameshift Mutations - causes the reading frame for codons to change.
Can result from deletions of nucleotides from the DNA sequence or from insertions of nucleotides into the sequence.
Either way, it shifts the reading frame in translation and results in a completely different sequence of amino acids being constructed.
Note that inserting or deleting 3 bases in the DNA wouldn’t shift the reading frame, it just adds or removes an amino acid.
Type 2: Chromosomal Mutations
Translocation
A segment of DNA moves from one part of the genome to another, usually non-homologous chromosome.
If it ends up in the middle of a gene, it can be transcribed, translated and form a “fusion protein” as seen in some types of leukemia.
Inversion
A segment of DNA reverses its orientation in the chromosome which can disrupt the gene or affect control of transcription.