A technique called polymerase chain reaction (PCR) makes this rapid cloning possible. PCR allows DNA from a specific region of the genome to be amplified by a billion-fold. In deceased individuals, we know that 50 percent of the DNA inherited from the parents is inherited, with the rest being unique to the new individual.
The genome is huge and recombination takes place almost randomly and also pcr can only amplify tiny lengths of dna. Also there are vast numbers of viral sequences scattered around the genome so as only half of the parental dna goes to the child and a quarter to the next generation and one eigth to the next generation etc I am sure that getting an exact unknown sequence by inference will be impossible