A X Chromosome Test is a DNA test, to be conducted between two sisters in order to establish a parental relationship. Are you sisters with different mothers who need to find out if they have the same father? If this is your case, the X chromosome test is the ideal DNA test for you. This test is based on the analysis of the X chromosome profile and uses 10 genetic markers.
The X chromosome DNA test determines if two sisters or two half-sisters descend from the same paternal line, even when the father’s participation is not possible. The test can also confirm that the sisters are from the same paternal grandmother.
Boys have an X chromosome and a Y chromosome, while girls are equipped with two X chromosomes. In girls, one of the X chromosomes necessarily comes from their mother and one X chromosome is inherited from their father who himself inherited it from his own mother. Every girl child in a family receives the same X chromosome from his father.
As chromosome remains essentially unchanged from generation to generation, the study of their X chromosomes can verify whether two sisters are from the same biological father, even in the absence of their presumed father.
Who can participate in an X chromosome test?
In cases of alleged two half-sisters having two different mothers, the comparison of their two X chromosomes pairs suffice to determine if they share the same biological father. It is not necessary to have the DNA samples of their respective mothers. However, this does not allow one to confirm the identity of the alleged father. The identity of the father could be confirmed by analyzing the DNA of the paternal grandmother as well.
If both are presumed sisters from the same mother, it is essential that the mother participates in testing of the X chromosome. In this case, the laboratory will be able to isolate the maternal X chromosomes and focus its research on the second X chromosome, inherited from the father. If it is not possible to have the maternal sample or if you are not sure that the two sisters have different mothers, it is advised to do a fill sibling DNA test instead.
X chromosome test results and reliability:
The test results are very clear. If the two sisters or half-sisters do not have similar X chromosomes, one can conclude that they have no chance to have the same biological father. If the X chromosome profiles coincide, paternity is 100% confirmed with the paternal X chromosome lineage. Meaning: The sisters share the same biological father.
When the grandmother participated in the test, the test results may provide additional information on the identity of the father. If the two sisters or half-sisters do not have X chromosomes comparable to those of their alleged paternal grandmother, we can conclude that they have no chance of being from this biological paternal grandmother. If the X chromosome profiles coincide, paternity is 100% confirmed within the paternal X chromosome bloodline: they are descended from their alleged paternal grandmother and thus the alleged father.
This test should not be performed if there is a chance that the biological father is a presumed father’s brother or cousin. Similarly if both mothers of two half-sisters are from the same family. In these particular cases, the test results of the X chromosome could be skewed because the X chromosomes of the alleged parents would be the same. In these cases i’s better to take a full sibling DNA test.