**Core Concept**
Restriction fragment length polymorphism (RFLP) is a technique used to detect genetic variations by analyzing the length of DNA fragments generated after restriction enzyme digestion. This method relies on the presence of polymorphic restriction sites within a gene or its regulatory regions.

**Why the Correct Answer is Right**
RFLP is a valuable tool for identifying mutations, such as those found in sickle cell anemia (HbS), where a single nucleotide substitution (Glu6Val) creates a new restriction site for the enzyme MstII. This technique has been extensively used in forensic science, paternity testing, and genetic mapping. The process involves digesting DNA with a restriction enzyme, separating the resulting fragments by gel electrophoresis, and analyzing their lengths.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because RFLP is not typically used for identifying chromosomal abnormalities such as trisomy 21 (Down syndrome). Other cytogenetic techniques, like karyotyping, are more suitable for this purpose.

**Option B:** This option is incorrect because RFLP is not a common method for detecting viral genotypes. Polymerase chain reaction (PCR) and sequencing are more commonly used for this purpose.

**Option C:** This option is incorrect because RFLP is not primarily used for identifying bacterial species. Techniques like 16S rRNA sequencing and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry are more commonly used for bacterial identification.

**Clinical Pearl / High-Yield Fact**
RFLP has been instrumental in identifying genetic mutations associated with various diseases, including sickle cell anemia, cystic fibrosis, and Huntington's disease.

**Correct Answer:** C. HbS (Sickle cell anemia)