Do close relatives share identical D.N.A.?

Only identical twins would share identical D.N.A. profiles. The probability that two unrelated individuals would share identical D.N.A. profiles by chance would be in the order of 1 in 1 billion. An individual would have half of their D.N.A. components identical to each natural parent. The potential to share identical D.N.A. components with a relative would diminish as the blood relationship becomes more distant.

How reliable is D.N.A. testing?

D.N.A. testing is one of the most reliable forms of forensic evidence. This is due to the nature of the regions of D.N.A. examined, which vary greatly from one individual to another. D.N.A. reference samples are taken and processed in duplicate to eliminate the possibility of error and control samples processed with all crimestains to eliminate the possibility of contamination.