Skin Color in a Certain Species of Fish Is Inherited

Multiple Choice

Skin color in a certain species of fish is inherited via a single gene with four different alleles. One fish of this type has alleles 1 and 3 (S₁S₃) , and its mate has alleles 2 and 4 (S₂S₄) . If each allele confers a unit of color darkness such that S₁ has one unit, S₂ has two units, and so on, then what proportion of their offspring would be expected to have five units of color?

A) 1/4
B) 1/8
C) 1/2
D) 0