Coat colors of dogs depend upon the action of at least two genes. At one locus a dominant epistatic inhibitor of coat color pigment (I-) prevents the expression of color alleles at another independently assorting locus, producing white coat color. When the recessive condition exists at the inhibitor locus (ii), then alleles of the other locus may be expressed, iiB- producing black and iibb producing brown. When dihybrid white dogs (meaning heterozygous for both gene pairs) are mated together, determine (a) the phenotypic proportions expected in the progeny, (b) the chance of choosing, from among the white progeny, a genotype homozygous at both loci.