What effect will inbreeding tend to have on genotypic frequencies in a population?

The correct option is C It will increase the frequency of homozygous genotypes.

Inbreeding increases the frequency of homozygous genotypes and decreases the frequency of heterozygotes. It may or may not increase the frequency of genotypes that produce a dominant phenotype. The key term here is homozygous vs heterozygous and not dominant vs recessive.