= Jukes-Cantor model
{c}
{title2=$P_{ii}(t)=\tfrac14+\tfrac34e^{-4qt}$}
The <Jukes-Cantor model> is a symmetric four-state <continuous-time Markov chain> for <DNA> evolution. Each change to a specified different base has rate $q$, so the total rate of actual changes is $3q$. Its same-base probability is $1/4+(3/4)e^{-4qt}$ and its probability for one specified different base is $(1/4)(1-e^{-4qt})$. The probability of any mismatch is three times the latter, tending to $3/4$ at long times. Distinguish the exponent parameter $4q$ from the actual per-site <mutation rate> $3q$ when fitting this model.
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