# How many markers or loci are used in forensic DNA profiling and the effect of the DNA sequencing?

I am reading the Wikipedia page on DNA profiling, specifically the STR analysis. It says the DNA profiling relies on 20 or so loci matching. It also gives an account of finding false identification. But that account was published in 2008. What is current state of art on DNA profiling? How many loci are used? Do we still need a database for constructing the probabilistic distribution of matching? I am particularly interested in the move toward DNA sequencing, how does that affect the profiling and matching probability calculation.

Suppose we sequence the whole available sample not restricted to particular loci.

1. When we have a single clean ample, is it true the probability of matching bounded by the probability of monozygotic twins resulting in the mismatching probability very close to $$1/2$$ of the monozygotic twin probability? The latter probability across all population is about $$0.002$$. It this upper bound reachable?

2. When there are admixture of several people/suspects' DNA in a sample and all the DNA (all 24 chromosomes) are intact.

3. When there are admixture of several people/suspects' DNA in a sample and some (the word covers the whole spectrum of degree/proportion) DNA's are damaged/missing.

4. In all the above cases, does the extraneous information such as gender, race/ethnicity affect the matching probability? I suppose the degree of effect increases in the order case 1 < case 2 < case 3.

• Hi @hans thanks for your question. Could you define your line of investigation more clearly? Things have moved to sequencing but it is context specific.
– M__
Jun 13 '20 at 13:38
• @Michael: Sorry for the late response. Thank you for your constructive comment. I have edited my question. I am indeed particularly interested in the impact of sequencing, as you mentioned, on DNA profiling.
– Hans
Jul 4 '20 at 18:52
• Thanks @Hans ..
– M__
Jul 4 '20 at 21:15
• @Michael: You are welcome. Will you be interested in providing an answer?
– Hans
Jul 4 '20 at 22:29