AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

Kinds of point mutation

KINDS OF GENE MUTATION

Base pair (nucleotide pair) substitutions

Transitions

• Mutations resulting from tautomeric shifts in the bases of DNA involve the replacement of a purine in one strand of DNA with the other purine (A <—> G) and the replacement of a pyrimidine in the complementary strand with the other pyrimidine (C <—> T). Such base pair substitutions are called transitions.
• Example: Four different transitions are possible

A•T —> G•C

G•C —> A•T

T•A —> C•G

C•G —> T•A

Transversions

• Purine replaced by a pyrimidine, or pyrimidine replaced by a purine are called transversions.
• Example: Eight different transversions are possible.

A•T —> C•G

A•T —> T•A

G•C —> T•A

G•C —> C•G

C•G —> A•T

C•G —> G•C

T•A —> G•C

T•A —> A•T

Frameshift mutations

• In this type of mutation, one or a few base pairs are inserted or deleted.
• Base-pair additions and deletions are collectively referred to as frame-shift mutations, because they alter the reading frame of all base pair triplets in the gene distal to the mutation.