In guinea pigs, black coat color is dominant over white coat color. The
of a mating between two heterozygous black guinea pigs would probably show a
phenotype ratio of

If they are both heterozygous black guinea pigs they both carry the allele for white fur. Therefore, the phenotype ratio would be 3:1 (75% offspring will be black furred, and a 25% it will be white furred). You can figure this out by using a punnet square too.