The requirement of the mother's DNA in such tests merely makes the testing easier and the process not as lengthy. However, when it comes to testing without the mother's knowledge or permission, the question is whether or not it is legal or ethical.
A father can easily get a home paternity test or even take a child he suspects is his (or not his) and have samples taken and sent to a lab. This is easy to do if the man has time alone with the child. It is also legal for a man to get DNA paternity testing done without the mother's consent, so long as he has joint custody of the child, as only a legal guardian can consent to the test if the child is a minor. This makes it easier for him to get the test results he needs, whether he wants to prove he is the father or that he isn't the father.
Of course, the question of whether or not it is ethical for a man to have a paternity test done without the mother's knowledge or consent is also a legitimate one. This may be a matter of personal opinion. If he feels that he is paying support for a child that is not his and the mother will not agree to a test, then perhaps he is justified. If he wants to have access to a child he is certain is his, then he may also be justified. Perhaps he wants to cheat on the test in order to get out of paying child support. That is just unethical any way you look at it.
The final verdict in this situation is that the father can get DNA paternity testing done without the mother's consent or permission as long as he shares custody of the child. This means that any man who wants to determine paternity, but is not considered a legal guardian must have the mother's permission to conduct the test. If she won't give it, then he is out of luck. When it comes to the father doing the test, while he can do so as the legal guardian, he cannot take a sample of the mother's DNA without her permission. As stated above, the mother's DNA is not necessary, but it does make the testing easier. Whether a man does the testing at home or does legal paternity testing so that it can stand up as evidence in court, as a legal guardian he is well within his rights to do so.
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