C. Probe.
A probe is a DNA molecule used in hybridization reactions to detect the presence of a particular gene in separated DNA fragments.
In molecular biology, hybridization refers to the process of complementary base pairing between DNA or RNA molecules. Probes are short, single-stranded DNA or RNA molecules that are designed to be complementary to a specific target sequence of interest. The probe is labeled with a detectable marker, such as a radioactive or fluorescent tag, which allows for the visualization or detection of the probe-target hybridization.
In the context of detecting a specific gene in separated DNA fragments, the probe is typically designed to be complementary to a specific region or sequence within the gene of interest. During hybridization, the probe will bind specifically to the complementary sequence in the DNA fragments of interest, allowing for their detection.
Options A (plasmid) and B (vector) refer to DNA molecules used as carriers or vehicles for the replication and propagation of foreign DNA sequences in host cells. While plasmids and vectors are essential tools in molecular biology, they are not specific to the detection of genes in hybridization reactions.
Option D (blot) refers to a technique used to transfer and immobilize DNA or RNA fragments onto a solid support (such as a membrane), which allows for subsequent hybridization and detection of specific sequences using probes. Blotting techniques include Southern blot (DNA), Northern blot (RNA), and Western blot (protein). While a blotting technique may involve the use of a probe, it is not specifically the DNA molecule used in the hybridization reaction.
Therefore, the correct answer is C. Probe.
