How frequently are Autosomal and X-STRs multistep mutations perceived as single-step?

Short tandem repeats (STRs) incur in length mutations that involve the loss or gain of repeats. STR mutation rates are usually estimated considering the rates of observed Mendelian incompatibilities in one generation familial configurations. When considering multistep mutations, for the autosomal and X-chromosomal modes of genetic transmission, underestimations are inevitable when using this approach (MIA), due to the occurrence of mutational events deceptively perceived as involving fewer steps.
Source: Forensic Science International: Genetics Supplement Series - Category: Forensic Medicine Authors: Source Type: research