Mutations & Genetic Engineering

A change in the nucleotide sequence of the genome of an organism Mutation A change in the nucleotide sequence of the genome of an organism

A mutation that changes one base Substitution A mutation that changes one base Possible outcomes: New codon codes for the same amino acid – silent New codon changes the amino acid – missense Sickle cell anemia New codon codes for a stop codon – non sense

Frameshift Mutations A change in the reading pattern of the DNA Causes: Deletions Sections of DNA are missing Cystic Fibrous Tay Sacs Insertions Mutations in which an extra base is inserted Crohn’s disease

Chromosomal Mutations Involves changes in the number or structure of chromosomes Deletion- loss of all or part Example: Williams Syndrome Duplication – segment is repeated Huntington’s disease Inversion – orientation is in the reverse direction Translocation – two non homologous chromosomes exchange segments The most common mutation, ΔF508, is a deletion (Δ signifying deletion) of three nucleotides[39] that results in a loss of the amino acid phenylalanine (F) at the 508th position on the protein.  The HTT mutation that causes Huntington disease involves a DNA segment known as a CAG trinucleotide repeat. Normally, the CAG segment is repeated 10 to 35 times within the gene. In people with Huntington disease, the CAG segment is repeated 36 to more than 120 times. This altered form, called mHtt (mutant Htt), increases the decay rate of certain types of neurons. Regions of the brain have differing amounts and reliance on these type of neurons, and are affected accordingly.[7] Generally, the number of CAG repeats is related to how much this process is affected, and accounts for about 60% of the variation of the age of the onset of symptoms.