These tests are vital in helping an individual beat the odds or overcome some of the problems they could be facing.Genetic testing can be performed in three different methods.For all relationships additional contextual and genealogical information is required to confirm the nature of the relationship.
The 23and Me health and trait reports are only available in certain countries.
The tests from Family Tree DNA, Living DNA and My Heritage are sold worldwide.
In some cases Y-DNA and mt DNA data may also be of help.
For autosomal DNA testing one should always test the oldest generations first wherever possible - your parents, grandparents (if you are lucky), aunts and uncles.
For relationships at the 4th cousin once removed to 5th cousin level you may need to test 10 to 20 or more first and second cousins and see how much autosomal DNA they share with a potential 4th cousin once removed or a potential 5th cousin in order to have sufficient data to generate a statistically significant average amount of autosomal DNA that is shared among the entire group, assuming that you are dealing with a non-endogamous population.
See Tim Janzen's summary at for an example of this type of quantitative approach.
By testing yourself as well as your parents you will be able to determine which segments have been inherited from which parent, and you will also be able to rule out coincidental (Identical by state) matches.
A two-parent/child trio also provides the best results for the purposes of phasing and chromosome mapping.
This type of test aims to identify any and all changes saw in chromosomes, proteins and in the genes of an individual.
In other words genetic testing can detect an array of medical and health problems, even while a child is still in utero.