  We analytically and numerically study the probabilistic properties of
inverted and mirror repeats in model sequences of nucleic acids. We consider
both perfect and non-perfect repeats, i.e. repeats with mismatches and gaps.
The considered sequence models are independent identically distributed (i.i.d.)
sequences, Markov processes and long range sequences. We show that the number
of repeats in correlated sequences is significantly larger than in i.i.d.
sequences and that this discrepancy increases exponentially with the repeat
length for long range sequences.
