The two X chromosomes present in females can
recombine during meiosis in the same way as the autosomes. In the
case of the paternally-inherited X chromosome in female offspring
and both the X and the Y chromosome in male offspring, almost the
entire chromosome is passed from parent to child unchanged, and
recombination only occurs within two small regions at the distal
ends of the chromosomes known as the pseudo-autosomal regions
(PAR). Currently, no STR markers utilized for forensic purposes
exist within these regions. Therefore, additional considerations for
linked markers are necessary during the interpretation of X and Y
STR results (see Section 4).