A number of STR markers can be tested on the Y-DNA. The more markers that are tested, the more discriminating the matches when comparing to other individuals.
For example, comparison of 12 markers alone is generally not powerful enough to distinguish family lines and can give inconclusive results. The more markers that are available for comparison, the more discriminating the comparison becomes.
There are two major advantages for comparing more markers:
1. To prevent false positives
2. To obtain conclusive results
Scenario:
Mr. Jones has been studying his family’s ancestry for several years and has started a “Jones” family study based in Arizona. He is interested in confirming that his family line is linked to a “Jones” line in New York. Although there are rumours that the two lines are related, Mr. Jones does not have the paperwork to prove this link. Mr. Jones is also interested in finding out whether his line is linked to any other Jones lines worldwide.
Mr. Jones had previously chosen to test just 12 markers. After testing, he uses the 12 markers to search the DNA database and finds out that he is a perfect match to the Jones line in New York. However, he also finds that he has a perfect match to over 200 individuals in the database, and over half of them do not even share his surname. How is this possible? Does it mean that he is related to everyone who matches him at the 12 markers? No, this simply means that data from only 12 markers is not powerful enough to distinguish Mr. Jones from other family lines.
To clarify this, Mr. Jones decides to increase his markers to 20. He enters the results of his 20 markers into the database and this time narrows down the number of matches. In fact, now, only 18 people match him perfectly at his 20 markers, including the Jones line in New York. Surprisingly, many of the individuals who used to match perfectly at 12 locations only match at 14 or less out of the 20 locations tested, confirming that there is no familial link with most of the 200 individuals identified in the 12 marker test (more than 3 mismatches indicates that two family lines are not closely related).
To further clarify the findings, Mr. Jones decides to upgrade to a 44 marker test. This time, he finds out that he is a perfect match at all 44 markers to only two lines, a Jones line in England, and a Jones line in the United States. After contacting the two lines and comparing paperwork and stories, Mr. Jones was able to confirm that his line was indeed definitely linked to both lines and he is now able to add both new lines to his family tree.
Surprisingly, Mr. Jones was also able to find out that only 43 out of the 44 markers matched with the Jones line in New York. This confirms that although the Jones line in New York is related to his line, they are likely more distantly related.
Mr. Jones also discovered that he had a close match to 4 other Jones lines (43 out of the 44 matched) and he is now pursuing the possibility that the 4 other lines are also distantly related to him (MRCA analysis dictates that 1 mutation occurs every 500 generations, and thus we would detect a mutation every 12 generations with the 44 marker test).
Mr. Jones is now trying to recruit more Jones males from throughout Europe to try to reconstruct and relink his family line.
Conclusion:
12 markers were not discriminating enough for Mr. Jones to pinpoint his family lines. After increasing to 20 markers, Mr. Jones was able to obtain more useful information and was able to eliminate false matches generated by the 12 markers. However, after increasing to 44 markers, Mr. Jones was able to pinpoint the people that he was looking for and was furthermore able to accurately answer his questions about his relationship to the Jones line in New York. Mr. Jones can continue to carry on his research, and as more and more people globally are tested and are added to the database, Mr. Jones will be able to reconstruct his family line in great detail and re-unite with Jones worldwide who are descendents of his family line.
