The loci P and Bz are 36 m.u. They are apart, on the same arm of a chromosome. A paracentric inversion occurs, which does not include either of the loci, but spans about 1/4th of the region.
a) When the inversion is heterozygous, crossing over events within the inversion will produce inviable products. Since, the paracentric inversion spans about 25% of the region between P and Bz, it will reduce the recombination frequency between the two loci.
Thus, the reduction in recombination frequency would be 1/4th of 36 m.u. This is equal to 9%.
Hence, the observed recombination frequency would be 27%.
b) When the inversion is homozygous, the products of crossing over within the inversion will be viable.
Hence, the observed recombination frequency would be 36%.