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Y-Chromosome DNA Testing

Determining If Two Or More Males Are Related

The Y-chromosome test is useful for males who need to find out whether they are related to another male along the same male lineage. For example, a grandson and his grandfather will have the same Y-chromosome. A nephew will have the same Y-chromosome as his uncle (father’s brother), as well as all of his uncles sons (male cousins). A male will have the same Y-chromosome as all males which have the same common male ancestor as himself. Thus, this test is very powerful for determining male progenitor relationships, and it helps to solve the question of whether two males are related along the male line.

About Chromosomes

Chromosomes are paired threadlike “packages” of long segments of DNA contained within the nucleus of each cell. In humans there are 23 pairs of chromosomes. In 22 pairs, both members are essentially identical, one deriving from the individual’s mother, the other from the father. The 23rd pair is different. In females this pair has two like chromosomes called “X”. In males it comprises one “X” and one “Y”. Therefore,  a person’s sex (male or female) is determined by the X and Y chromosomes. A female has 2 X-Chromosomes and a male has an X and a Y-Chromosome. When a child is conceived it gets one chromosome from its mother and one chromosome from its father. The chromosome from the mother will always be an X, but the chromosome from the father may be either X or Y. If the child gets the X she will be a girl, if the child gets the Y he will be a boy.

Testing the Y-Chromosome

While paternity testing is considered to be the most conclusive way to tell if the male is the father of a child, a Y-Chromosome test between a possible father and a male child can also give us the answer. However, one must be very careful as false results can occur. This can happen if the possible father of the child could be any one of a number of male-related male relatives. So, if two possible fathers are siblings who share the same father, or cousins who share the same grandfather, then a Y-Chromosome test would match both men. However, if the two possible fathers are not related, then the Y-Chromosome test will be true.

Example: A male child is adopted to a family and years later finds that he might have a male sibling form the same father, or a cousin from his fathers’s brother. (His cousin would have to have the same grandfather, not the same grandmother.) Then, we could perform a Y-Chromosome test and tell if they do indeed share the same progenitor.

Example: Two brothers have the same mother and are not certain if they have the same father. A Y-Chromosome test will give them this answer.  (A mitochondrial test will also conclusively tell them if they have the same mother.)

Extended Testing Using Y-Chromosome

If a paternity test is inconclusive due to a genetic mutation or other issue, a Y-Chromosome test can be performed on a male and his male child to complete the results. However, we need to make sure any other possible father is not related to the tested male on his father’s side or we could get false results.

For more information, or a free consolation, please email or call us.

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