Final answer:
The correct answer is pseudodominance. It refers to the expression of a recessive allele due to the deletion of the corresponding allele on the homologous chromosome, and it should not be confused with epistasis, pleiotropy, gene dosage, or unmasking. Therefore, the correct option is B.
Step-by-step explanation:
A deletion in one homolog that allows the phenotypic expression of recessive alleles in the other homolog is an example of pseudodominance. This term refers to the situation where a normally recessive allele is expressed phenotypically because the corresponding allele on the homologous chromosome has been deleted. It is not an example of epistasis, which is the masking of the expression of one gene by another gene, nor is it pleiotropy, where one gene affects multiple phenotypic traits. Gene dosage effects occur when the number of copies of a gene influences the phenotype, which is not the case here. Lastly, unmasking generally refers to the expression of recessive alleles when an individual is homozygous for those alleles.
An example of epistasis is seen in mice pigmentation, where a mouse with a recessive c allele at a certain locus is unable to produce pigment and hence is albino, regardless of the allele present at another locus (A). The gene C is said to be epistatic to gene A because its expression (albino phenotype) masks the expression of gene A (coat color).