Correct answer: (a) Studying the evolutionary relationships among various species of fauna
Explanation
- A
Studying the evolutionary relationships among various species of fauna
Studying evolutionary relationships among species. Microsatellites are classic population-genetic and phylogenetic markers.
- B
Stimulating 'stem cells' to transform into diverse functional tissues
Stimulating stem cells. Unrelated.
- C
Promoting clonal propagation of horticultural plants
Clonal horticulture. Micropropagation, not microsatellite DNA as the tool named here.
- D
Assessing the efficacy of drugs by conducting series of drug trials in a population
Drug-trial efficacy. Clinical, not this marker.
Summary. Official key is (a). Microsatellite DNA (SSR / STR) — short tandem repeats — is used to measure relatedness, population structure and evolutionary relationships. It is not a stem-cell stimulus, a cloning protocol, or a drug-trial design.