A chemical that resembles a naturally occurring * purine or * pyrimidine base to the extent that it may be incorporated into a DNA molecule during replication. However such analogues are less specific in their pairing properties. For example, an analogue of adenine may pair with cytosine as well as thymine. Over two replications this would result in a point mutation, with a cytosine:guanine pair replacing an adenine:thymine pair on one of a pair of homologous chromosomes. Base analogues may also be incorporated into RNA during RNA synthesis, e.g. thiouracil and fluorouracil can replace uracil. Such changes may have various physiological effects. See 5-bromouracil. |
