Background
The familiar double-helix model of DNA was developed by Francis Crick & James Watson in 1953, and the DNA fingerprint was discovered by accident in 1985 by Alec Jeffreys.
The human body has 100 million million cells. A cell is the basic unit of structure in living things. Chromosomes are tiny bodies in a cell which carry the genes. A gene is a piece of DNA (deoxyribonucleic acid) which carries the hereditary information.
Only males have the Y-Chromosome which is passed from father to son usually in identical form from one generation to the next. Occasionally, a change (which is called a mutation) occurs between a father and son. These mutations can be compared to determine likelihood of testers' relation and estimate the time back to their Most Recent Common Ancestor (MRCA). As surnames are passed from father to son through the generations, DNA testing is confined to men with the same surname (or phonetically similar surnames).
While Y-DNA is limited to males, DNA testing as a whole is not an all-male preserve. Female lineage can be traced using Mitochondria instead of the Y-Chromosome, but the patronymic nature of Irish surnames means that this form of testing is not useful in Irish genealogy.
DNA may be sampled in a number of ways. The easiest method is to take a minute sample of skin cells from the mouth by gently brushing the inside of the cheek with a small sterile brush. The process does not hurt. The test is self-administered using what looks like a travel toothbrush which is then popped into the post for analysis. A blood sample is not required!
The human body has 100 million million cells. A cell is the basic unit of structure in living things. Chromosomes are tiny bodies in a cell which carry the genes. A gene is a piece of DNA (deoxyribonucleic acid) which carries the hereditary information.
Only males have the Y-Chromosome which is passed from father to son usually in identical form from one generation to the next. Occasionally, a change (which is called a mutation) occurs between a father and son. These mutations can be compared to determine likelihood of testers' relation and estimate the time back to their Most Recent Common Ancestor (MRCA). As surnames are passed from father to son through the generations, DNA testing is confined to men with the same surname (or phonetically similar surnames).
While Y-DNA is limited to males, DNA testing as a whole is not an all-male preserve. Female lineage can be traced using Mitochondria instead of the Y-Chromosome, but the patronymic nature of Irish surnames means that this form of testing is not useful in Irish genealogy.
DNA may be sampled in a number of ways. The easiest method is to take a minute sample of skin cells from the mouth by gently brushing the inside of the cheek with a small sterile brush. The process does not hurt. The test is self-administered using what looks like a travel toothbrush which is then popped into the post for analysis. A blood sample is not required!
DNA Fingerprint Testing
The accuracy of the Y-Chromosome test, and reliability of the results, is directly related to the number of reference points (called markers) used in the analysis. The lowest useful resolution is 12 markers, and this was the world's first commercial DNA test developed by FamilyTreeDNA in the U.S.A. in March 2000. However, whilst the 12 marker test easily differentiates between Africans, Eastern Europeans etc., it lacks the fine resolution required to differentiate between the more recently arrived Western Europeans. Consequently, FamilyTreeDNA launched the 25 marker test in November 2001, and this was followed by the 37 marker test. This has been adopted as the global standard. In more recent times FTDNA have added a 67 Marker and larger tests to their facilities.
It should be obvious at this point that Y-Chromosome testing is an emerging science!
The point in the Y-Chromosome where the marker is tested is called a DYS number. The test value assigned to each DYS is called an STR (Short Tandem Repeat).
The raw data table of 25 DYS STRs is called a haplotype. Exact or nearly exact matches of data establish the haplotype of the common ancestor. The next most important factor is the MRCA number (Most Recent Common Ancestor), which is the estimated number of generations to the occurrence of the most recent common ancestor of two people.
It should be obvious at this point that Y-Chromosome testing is an emerging science!
The point in the Y-Chromosome where the marker is tested is called a DYS number. The test value assigned to each DYS is called an STR (Short Tandem Repeat).
The raw data table of 25 DYS STRs is called a haplotype. Exact or nearly exact matches of data establish the haplotype of the common ancestor. The next most important factor is the MRCA number (Most Recent Common Ancestor), which is the estimated number of generations to the occurrence of the most recent common ancestor of two people.