According to Mendel Law of segregation all offspring in F1 generation will white wool. However, in F2 generation three will be white wool and only one offspring will be spotted wool.
Phenotype (parental generation) White wool x spotted wool
Genotype TT tt
F1 generation Tt, Tt,Tt, Tt (white wool)
Self cross Tt x Tt
F2 generation TT, Tt, Tt, tt
white wool = 3
spotted wool = 1