An Introduction to Y-DNA
The Y chromosome is only found in males and is passed from father to son along the paternal line. This is unlike the autosomal DNA (atDNA), which is the most commonly tested type and comes from the other 22 chromosomes. Effectively your atDNA becomes a half and half mixture inherited from both parents, thus diluting the DNA acquired from each generation. This is very useful for researching back several generations across all of the family lines but is unable to peer very far back into the past. Y DNA, however, is passed in its entirety and like all DNA is built from 4 proteins Adenine, Thymine, Cytosine and Guanine (often abbreviated to A, T, C, G). The Family Tree DNA (FtDNA) Big Y 700 test reads the sequence of these proteins across millions of locations along the Y chromosome.
Although the Y chromosome is inherited in its entirety, occasionally there will be a natural variation when it gets copied to a new generation, for example an ‘A’ may change for a ‘T’ at a particular location. These variations occur quite slowly, approximately one change across the whole chromosome every 80 years or so (1 change every 3-4 generations). By mapping these changes geneticists have created a Y DNA family tree, assigning a person to a particular branch called a haplogroup, which eventually links back to an individual who left Africa many thousands of years ago!
Continue reading: Distribution of the Freeman Surname