You are studying coat color and number of toes in mice. you perform the following crosses:

cross 1: black, five-toed x white, six-toed gives: all black, six-toed progeny
cross 2: white, five-toed x black, six-toed gives: all black, six-toed progeny

a. for each trait (coat color and number of toes), state which is the dominant phenotype and which is the recessive phenotype.

 Dominant allele

Coat color =black

                Number of toes =six

                Recessive allele

White color

Five toes

Explanation:

Based on Mendelian law of independent assortment of genes  

The genes for   black coat and five toes are hetero zygote for the coat color and toes number. Likewise the gene for white coat and six toes

. The black coat color is a dominant /phenotype over the recessive white color, while the five toes is recessive  phenotype to the dominant six toes.

This is evident from the F1 and F2 generations where all the offspring were all black and six- toed.

If  the white  coat and five -toed  were  the dominant allele, then some of the offspring should  have appeared either as homo zygote or hetero zygote allele as  white with five –toes!!, in the F1- F2 generation assuming they were masked in F1 in the presence of black coat and six toes, so far  they can segregated independently of one another.

"do a testcross with a homozygous recessive plant."