In guinea pigs, fur color is an autosomal recessive Mendelian trait. A dominant gene "B" in guinea pigs is responsible for making the fur black, whereas a recessive allele "b" makes the fur white. Two guinea pigs were mated to produce the following number of offspring: 

Guinea pigs with black fur= 9 

Guinea pigs with white fur=3 

What is the possible genotype of the parents of this offspring?