Skin color in a certain species of fish is inherited via a gene with four different alleles. Each allele confers a unit of color darkness such that having allele S1 confers one unit of color, S2 has two units, S3 has three units, and S4 confers four units. A fish of this type has the genotype S1, S3, and its mate has the genotype S2S4. What proportion of their offspring would be expected to have five units of color

25% of the progeny with genotype S3S4 is expected to express 5 units of color

Explanation:

Available data:

Cross:

Parentals) S1 S3   x   S2S4

Gametes) S1   S3      S2     S4

Punnett square)       S1           S3

                      S2     S1S2      S2S3

                      S4     S1S4      S3S4

F1) 1/4 = 25% of the progeny is expected to be S1S2, expressing 3 units of color ⇒ allele S1 provides one unit, allele S2 provides two units of color

    1/4 = 25% of the progeny is expected to be S2S3, expressing 5 units of color ⇒ allele S2 provides two units, allele S3 provides three units of color

    1/4 = 25% of the progeny is expected to be S1S4, expressing 5 units of color ⇒ allele S1 provides one unit, allele S4 provides four units of color

    1/4 = 25% of the progeny is expected to be S3S4, expressing 7 units of color ⇒ allele S3 provides three units, allele S4 provides four units of color

25% of the progeny with genotype S3S4 is expected to express 5 units of color

her affection for her parents makes her an especially sympathetic character.