Which of the following is not a cause of point mutation?
Ans. a. Paracentric inversion (Ref: Robbins 9/e p138, 160, 8/e p138, 160; Lippincot 5/e p433-434)"Inversion refers to a rearrangement that involves two breaks within a single chromosome with reincorporation of the inverted, intervening segment. An inversion involving only one arm of the chromosome is known as paracentric. If the breaks are on opposite sides of the centromere, it is known as pericentric. Inversions are often fully compatible with normal development."- Robbins 9/e p160, 8/e p160 Point MutationsReplacement or changes in single baseQTransitionTransversionPurine - PurineQ Pyrimidine - PyrimidineQPurine PyrimidineQ Pyrimidine - PurineQ Effects of point mutationSilent Mutations:No apparent effect due to change in 3rd nucleotide of genetic code (Wobble hypothesis)QThe codon containing the changed base codes for the same amino acidQExample: 67th position of B chain of HbAQNormalValineMilwaukeeQGlutamateBristolQAspartateSydneyQAlanineMissense mutations:The codon containing the changed base codes for different amino acidQAcceptable: Change in amino acid does not alter function of protein, Ex: Hb Hikari b-61: Asparaginase for lysineQPartially acceptable: Change in amino acid interferes with normal function. Ex: HbS/Sickle cell anemia b-6: Valine for glutamic acidQUnacceptable: Result in totally non-functional protein, Ex: HbM (Boston) a-58: Tyrosine for histidineQNonsense mutations:The codon containing changed base may become the termination codonFrame-shift muations:Addition or deletion of a base can cause aleration in the frame of m-RNA.
Paracentric inversion
Deletion
Substitution
Insertion
Molecular Genetics