TheX-chromosome normally always appears as one of a pair, though there are exceptions. In females two X chromosomes appear together- one chromosome inherited from the mother and one chromosome inherited from the father. The case is somewhat different in normal males, whereby the X-chromosome is always inherited from the mother and the Y-chromosome from the father. Profiling this gene is important in genetic testing when one wants to find out if two females share the same father or not; however, in such a case, the mothers would have to be different as it would not be clear whether the mother or father passed the X-chromosome if they females shared the same mother. More information can be found on X-Chromosome Testing which will give insight into the nature of genetic testing to establish relationships between females.