Answer:
Let's have our alleles be J = dominant, j = recessive. And for fun let's make the dominant phenotype black coat, the recessive brown coat.
Heterozygous x homozygous recessive
= Jj x jj
Punnett square:
J j
j Jj jj
j Jj jj
Genotypic ratio: 2 Jj : 2 jj, or a one-to-one ratio of Jj to jj.
Phenotypic ratio: 2 black : 2 brown, or a one-to-one ratio of black to brown.
