DNA is organised into 46 chromosomes, 23 inherited from their mother and 23 inherited from their father. One chromosome, called the Y-chromosome, is only present in men and is transmitted from a father to his son unchanged. Y-chromosome testing involves the analysis of 17 genetic markers (called STRs) on the Y chromosome to produce a YSTR profile.

Common applications of the Y-chromosome test:

1. Genealogy: The Y-chromosome test can be used to provide evidence linking individuals to a common male line as they share the same Y-STR profile, or it can provide proof that they are not related. This type of test is often used in surname projects which involve large groups of individuals with a common surname who are interested in researching their ancestors.

2. Male relationship testing: In cases where the alleged father is unavailable for testing or deceased, a male can be tested against other potential male relatives such as his uncles (his father's brother's), his grandfather or his grandfather's brothers who share the same alleged male line.

3. Sibling testing: Y-chromosome testing can be used as an alternative (or additional) test, where both children are male, to determine if they could share the same father.

Note: Y STR testing can in some instances conclusively confirm that two people do not share a common male relative. Alternatively it can provide very useful information to support a common male inheritance - but the statistical significance of the results in such cases will not approach the levels achieved in standard paternity testing. Indeed, Y STR testing should not be regarded as an alternative to standard paternity testing, since all male blood relatives in a family will have the same YSTR profile.

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