Answer
10. d.
Recessive alleles for diseases will be expressed in double recessive genotypes.
Work Step by Step
Some autosomal recessive diseases are cystic fibrosis, and alkaptonuria. In autosomal dominant diseases like neurofibromatosis and Van Gierke's disease (glycogen storage D), the recessive allele is not expressed in the genotype N/n or V/v because it is dominated by the dominant gene -- N or V respectively.
