3. Point mutation in which there is deletion or addition of one base pair is termed as
(1) Deletion (2) Transition
(3) Transversion (4) Frame shift mutation
A point mutation involving deletion or addition of one base pair is termed as frame shift mutation [(4)]. This is the correct answer for the CSIR NET Life Sciences question, as such changes disrupt the codon reading frame during translation, leading to altered protein sequences downstream.
Option Explanations
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(1) Deletion: Refers to the removal of nucleotides from DNA, but alone it is too broad and does not specifically denote the effect of a single base pair change on the reading frame.
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(2) Transition: Involves substitution of a purine for another purine (A↔G) or pyrimidine for another pyrimidine (C↔T), preserving the reading frame without insertion or deletion.
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(3) Transversion: Describes substitution of a purine for a pyrimidine or vice versa (e.g., A↔C), which also maintains the codon frame unlike additions or deletions.
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(4) Frame shift mutation: Correctly identifies insertions or deletions of non-multiples of three bases, like one base pair, shifting the genetic code’s triplet reading frame and often producing nonfunctional proteins.
Mechanism of Frame Shift in Point Mutations
Point mutations include single base substitutions, insertions, or deletions. While substitutions like transitions and transversions typically cause missense, nonsense, or silent effects without frame shifts, a single base pair deletion or addition alters all subsequent codons. For CSIR NET preparation, recognize that frame shifts from one base pair changes exemplify indel mutations with severe phenotypic impacts, such as in diseases like cystic fibrosis. This distinction is crucial for exam questions on mutation types in molecular genetics.
