Answer:
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.
