Let BB/ Bb be the dominant color (black) of guinea pig and bb be the recessive trait which codes for white color of guinea pig.
i) The possible genotype of the parent pigs is Bb i.e. the animals are heterozygously dominant as they produced offspring in the ratio of 3: 1. The 25 of the black pigs have the gene BB whereas the rest 50 of the black pigs have genes Bb and the white pigs have bb.
ii) The trait coding for black color is dominant while the one coding for white is recessive.