Recombination fraction( frequency) in Homozygotes
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Your question stems from the confusion between measuring a recombination rate and the actual recombination rate.

In the A/A, B/B individuals you describe, recombinations still occur. Those recombination just don't affect linkage disequilibrium between the Aa and the Bb loci as there is no variance at those loci in the individuals you considered. There is therefore, no way to tell whether or a recombination event occurred in a specific case. You need genetic variance at both loci in order to have a linkage disequilibrium which can be affected by recombination. But it is not because you can't measure the recombination rate that recombinations does not occur.