For a new mutation arising in the XYZ gene designated XYZG287 there is a linked allele, QRS2 ~100,000bp away on the same chromosome. After 20 generations, what is the estimated linkage disequilibrium, D, observed between these two alleles? How long will it take to reach half the initial value? Assume recombination rate (r) is 1% for every megabasepair (Mbp).