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

MOLECULAR BASIS OF MUTATION

• The bases in DNA are not static.
• Hydrogen atoms can move from one position in a purine or pyrimidine to another position, for example from an amino group to ring nitrogen.
• Such chemical fluctuation are called tautomeric shifts.
• The ability of a molecule to exist in more than one chemical form is called tautomerism.
• The common keto forms of thymine and guanine will always pair with adenine and cytosine, respectively.
• The common amino forms of cytosine and adenine will always pair with guanine and thymine, respectively.
• The more stable keto forms of thymine and guanine and amino forms of adenine and cytosine may infrequently undergo tautomeric shifts to less stable enol and imino forms respectively.
• When the bases are present in their rare enol and imino forms, they can form adenine — cytosine and guanine — thymine base pairs.

• This will ultimately leads an AT to GC or a GC to AT base pair substitution.