In an asexual species, a beneficial allele and a deleterious allele are in linkage disequilibrium. The selection pressure for the beneficial allele is lower than the pressure of purifying selection, so the beneficial allele is being lost from the population. What is this an example of

selective interference

Explanation:

Natural selection acts on genes that are inherited together, which is the case for species of asexual reproduction (where genes are inherited together by clonal offspring).  In asexual species, linkage disequilibrium (i.e., non-random association of the alleles of different loci), can be understood in a similar mode in terms of population allele frequencies. Selective interference underlies the association between beneficial mutations and surrounding sites which are subject to deleterious mutations. It has been shown that asexual species adapt at a slower rate than species of sexual reproduction. In sexual species, selective interference could be bypassed through the mechanism of recombination during meiosis (although there is not conclusive evidence of this). In asexual species, different deleterious and beneficial mutations are generally fixed, whereas beneficial mutations are generally spread and fixed in species of sexual reproduction.