A mutation creates a dominant-negative allele of kinky gene. The kinky gene encodes a protein that forms a tetramer within the cell. If one or more of the subunits has the mutant structure, the entire tetrameric protein is inactive. This has the phenotype of a kinky tail in mice. In a heterozygous cell, if the proteins of both alleles are present at the same levels, what percent of the tetramers present in the cell will be active?

A. 6.25%

B. 12.5%

C. 100%

D. 50%

E. 0%