In rabbits, spotted coat (S) is dominant to solid color (s) and black (B) is dominant to brown (b). A true-breeding black spotted rabbit is mated to a true-breeding brown solid rabbit to produce a heterozygous F1 generation. Two F1 individuals are mated, and you do not see a 9:3:3:1 (black spotted: black solid: brown spotted: brown solid) ratio of offspring, but instead see that almost all offspring are a non-recombinant phenotype. This tells you that

Epistasis effect result into these offspring

Explanation:

Given

spotted coat (S) is dominant to solid color (s) and black (B) is dominant to brown (b)

Genotype of true-breeding black spotted rabbit BBSS

Genotype of  true-breeding brown solid rabbit bbss

Genotype of offspring BbSs

In normal crossing between BbSs and BbSs offspring of F1, should produce offspring in the ratio 9:3:3:1

But it does not happens in this case the simple reason could be  presence of Epistasis in which the alleles assort independently but do not express themselves because of the following reasons -

a) Interaction between two or more loci thereby resulting into new phenotypes

b) An allele at one locus masks effects of other allele at one or more loci

c) Allele at one locus modifies the effects of alleles at one or more other loci