The actual recombination rate is the number of observed recombination
events divided by the total number of events. Like flipping a coin, the
number of observed recombination events can be larger than 50%. That is,
the recombination fraction is a statistical measure; the 50%
recombination value for unlinked markers is the EXPECTED value which, in
an actual experiment, may be more or less than 1/2. In linkage
computations, some programs will not allow a value of greater than 50%
for the calculated recombination fraction. Other programs will allow
such a value, but a value greater than 50% usually implies an error in
the data set.