Answer:
50% of their children will have blond hair
Explanation:
Given ,
Allele for brown hair is represented by "B" and it is a dominant trait
While Allele for blond hair is represented by "b" and it is a recessive trait.
Genotype of Sally when it is given that she carries the recessive gene of blond hair - Bb
Genotype of Sally's husband who has has blond hair, which is a recessive trait - bb
Bb x bb
Bb, Bb, bb, bb
Out of four offspring two will have blonde color hair,
Thus, 50% of their children will have blond hair