Question

in a study of the evolution of dpta and dptb—diptericin genes encoding antimicrobial peptides that combat pathogens and foster beneficial interactions in fruit flies (drosophila)—researchers examined drosophila melanogaster resistance to pathogenic infection by pseudomonas, morganella, and acinetobacter species, bacteria common in the flies’ environments.
genotypes included flies identified by mutations deleting dpta, dptb, or both dpta and dptb (denoted type a, b, and ab, respectively). in conjunction with the observation that resistance to b. cepacia correlates with dpta activity but is not significantly affected by dptb activity, data in the graph of survival rates post-a. siccana infection suggest that

average survival of fruit flies following infection

graph of survival rate (% alive) over days after infection, with three lines: type a flies (solid line with triangles), type ab flies (dashed line with squares), type b flies (dotted line with circles)

12 □ mark to review
which conclusion of the text is best supported by data in the graph?
a dpta confers defense against a. siccana regardless of the presence of other dpt.

b dptb protects against only one bacteria species, whereas dpta protects against multiple species.

c dptb may have developed as a specific defense against a. siccana.

d defense against a. siccana is strongest when both dpta and dptb are present.

Explanation:

To solve this, we analyze the graph and options:

• Option A: The graph shows Type A flies (with DptA) have lower survival than Type AB or B? No, wait—wait, the graph's y - axis is survival rate. Wait, Type A flies (solid line) after infection: at day 10, survival is low, but Type AB (dashed - like) and Type B (dotted) have different. Wait, no—wait the key: Type A flies (solid), Type AB (dashed), Type B (dotted). Wait, the text says "by high activity data in the graph of survival rates post - A. sterile infection suggest that...". Wait, the question is which completion is supported. Let's check each option:
• Option A: "DptA confers defense against A. sterile regardless of the presence of other..."—but the graph: Type A flies (with DptA?) Wait, no, Type A flies: when infected, their survival rate. Wait, maybe misreading. Wait, the other options: Option C: "DptB may have developed as a specific defense against A. sterile"—but the graph shows Type B flies (with DptB) and Type AB (both DptA and DptB) and Type A (DptA). Wait, the survival of Type B flies (dotted) and Type AB (dashed) and Type A (solid). At day 10, Type B and AB have similar survival, Type A is lower. But the key is about DptB's development. Wait, the text mentions "mutations ablating DptA, DptB, or both DptA and DptB (termed types A, B, and AB, respectively)". So Type B has DptB, Type A has DptA, Type AB has both. The graph for A. sterile infection: Type B flies (with DptB) have better survival than Type A (with DptA) at some points? Wait, no, maybe the correct option is C? Wait, no—wait the option C says "DptB may have developed as a specific defense against A. sterile". Let's re - evaluate:
• Option D: "defense against A. sterile is strongest when both DptA and DptB are present"—but Type AB (both) and Type B (DptB) and Type A (DptA). If both are present (Type AB), is survival strongest? The graph: at day 2, Type AB and B have similar, Type A lower. At day 6, Type AB and B, Type A lower. At day 10, Type B and AB have similar, Type A lower. So maybe not D. Option C: DptB (in Type B flies) has survival similar to Type AB (both DptA and DptB) against A. sterile, suggesting DptB is specific for A. sterile. So Option C is supported. Wait, maybe I made a mistake, but based on the analysis of the graph and the options, Option C is the most reasonable as it suggests DptB's specific defense development.

Answer:

C. DptB may have developed as a specific defense against A. sterile