A short-tailed mutant of mouse was discovered. Multiple crosses of this mouse to normal mice produced 27 normal, long-talied mice and 25 short-tailed mice. A series of crosses among short tailed mice were made and and 21 short-tailed mice and 11 long-tailed mice were produced? Study these results and determine which phenotype is dominant and explain the ratios observed with regards to the genotypes of the parents in each cross.

Allele for short tail is a dominant phenotype.

Explanation:

In the second generation , the cross between a group of short tailed mice  produces either short tailed or long tailed species.

This means the short tailed mice must be having the allele for long tail trait but did not expressed it.

Hence, when two alleles are presents and one is expressed while the other is suppressed then allele expressing its trait would be the dominant phenotype.

Hence, the allele for short tail is a dominant phenotype.

Cross between two short tailed mice will be as follows

Ss * Ss

SS, Ss, Ss, ss

Out of four three are short tailed while one "ss" is long tailed.

the answer to your question is:

c. complementary base-pairing