X and Y chromosome tests are types of DNA tests often carried out between siblings, normally to determine whether or not they have the same father. Of course, the chromosomal characteristics of males and females means that the X and Y chromosome test are gender-specific.
We know that all males have a total of 46 chromosomes or 23 pairs of XY chromosomes (the Y chromosome is only present in males). Females on the other hand, had 46 chromosomes or 23 pairs of XX chromosomes. Of course, there are chromosomal abnormalities where people have extra chromosomes:
- Klinefelter‘s syndrome (one extra X chromosome in males),
- Turner’s syndrome (one X chromosome less in females),
- Edward syndrome (extra chromosome 18)
There have also been one or two documented cases of people with fewer chromosomes. However, let’s get back to the topic at hand.
Y chromosome testing
The Y chromosome is found only in males. It is inherited by male children from their father. The father would in turn, have inherited the Y chromosome from his dad and the inheritance pattern proceeds so forth. We can thus see that males from the same paternal lineage inherit the same Y chromosome and hence, their biological relationship can easily be confirmed by doing a Y chromosome test. Irrespective of their relationship – brothers, uncles and nephews, grandfathers and grandsons, fathers and sons – a Y chromosome test will accurately confirm whether two males are actually related because if they are they will have the same Y chromosome blueprint.
The Y chromosome test is therefore great to carry out instead of a paternity test. Imagine you have two brothers who think they do not have the same father. However, the father in question has died and because of this, the two brothers cannot carry out a paternity. They can in this case do a Y chromosome test. If the result shows they have the same Y chromosome profile, then they share the same father. The only drawback of the test is its inability to distinguish between male biological relatives. In this example given, two males with the same Y chromosome profile could be brothers as much as first cousins, father and son and so forth.
X chromosome testing
X chromosome testing can be done only between females. Usually it is females who need to know if they share the same biological father that do this test. For this test to be accurate however, we need to establish one important issue.
- Do the females share the same mother or do they have different mothers?
If they do not share the same mother, they can carry out an X chromosome test just between themselves. The test will show whether or not they share the same X profile. If they do, it means that have the same dad. This is because the X chromosomes they inherited from their mothers will be different (remember, we said they have different mothers?). Thus, if the result shows a match, then we can conclude that this match is because of the X chromosome they inherited from their common biological dad.
If the females tested have the same mom, the test requires the mother’s sample. This is because it will be hard to determine whether a matching X chromosome profile between two females with the same mother is due to the fact they inherited the same chromosome from their mother or because they inherited the same X chromosome from their father (Let’s remember that a mother could have passed on one of two X chromosomes from her X chromosome pair whilst the father could have passed only one X chromosome from his XY pair).
Both these types of DNA tests are extremely accurate and provide yes or no answers. In rare cases, there could be mutations which can compromise the results. However, these cases are rare.
Karl M McDonald is a freelance writer specializing in the field of DNA and genetics. More articles by the author can be found in the article repository for easyDNA. Click here to read more articles about DNA testing by this author.