Final answer:
Short tandem repeats (STRs) are the variable sequences used in DNA profiling, found in non-coding regions and often used for genetic mapping.
Step-by-step explanation:
The correct answer to the given question is 'a) Tandem'. Short tandem repeats (STRs) are variable DNA sequences that are very useful in DNA profiling, which is a technique often used in forensic science to assist in identifying individuals based on their unique DNA pattern.
These repeats are sets of nucleotides that are repeated in the non-coding regions of the DNA, typically in a head-to-tail manner.
The number of repeats can be highly variable among individuals, which makes them excellent markers for DNA fingerprinting and genetic mapping.