In mice, the black fur phenotype is dominant over the white fur phenotype. Two black fur mice are bred and have the litter shown below. What is the most likely explanation for the presence of the white fur offspring W. A mutation occurred

R. The female mouse escaped and mated with a white mouse. Then she came back to the cage and closed it before anyone noticed

F. Both of the parents are heterozygous

B. One of the parents is heterozygous