Answer:
Dominant
Explanation:
Let the allele for short tail trait be represented by "T" and allele for long tail trait be represented by "t"
When a short tailed mutant with genotype "tt" is mated with long tailed mouse, following offspring will be produced -
Tt * tt
Tt, Tt, tt, tt
so the ratio of short tailed and long tailed mouse is 1:1
Here it is given as 4:3 . Hence, there are chances that short tail trait is dominant
In the second generation , two short tailed mouse are crossed. The following offspring will be produced
Tt * Tt
TT, Tt, Tt, tt
The ration of short tailed and long tailed mouse is 3:1
Here it is given as 6:3 i.e 2:1 . Hence, short tail trait is dominant over long tail trait.