Alec Jeffreys used .......... as genetic marker.

The technique of isolating and sequencing the DNA is called DNA fingerprinting. This technique was developed by Alec Jeffrey in 1984. Generally, a small amount of DNA is obtained from the samples.  PCR technique is used to amplify the DNA molecules present in a small sample in order to obtain a large amount of DNA sequence for the test. This is followed by restriction fragment length polymorphism (RFLP). RFLP analysis is used to identify the repeated sequences by detecting a specific sequence pattern to the Variable Number Tandem Repeats which becomes that individual's DNA profile also called as genetic markers. Thus the correct answer is option D.