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Ancestry DNA Testing

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If the main reason why we research our past is to discover who we are, then it is not surprising that the implications of genetic research have become a fascination among many family historians in recent years. The fact that genetics may help prove, or disprove, who our ancestors are, or indicate that disparate family groups with the same surname do in fact all descend from the same pair of ancestors, is only part of this new area of interest. That we may now be able to know which of our traits and characteristics were passed on to us by ancestors now gone is an interesting prospect. And that we can now seriously consider what we might pass on to future generations could be a matter of considerable importance. At least, that is the theory.

According to one expert: 'Knowing our genetic profiles can help us fulfil our desires to add lasting meaning to human life.' However, that is probably doubtful. Nevertheless, many family historians are expanding their research to create family health histories that may point to disease-causing genes in their families.

Now for the science. Our bodies are made up of basic building blocks called cells. Each cell has a nucleus, which controls the cell's functions. Within the nucleus are two sets of chromosomes, 23 received from the mother and 23 from the father. Each chromosome is comprised of strings of DNA (deoxyribonucleic acid), which hold the blueprint (genome) of who we are. The DNA is arranged in the form of two strands wrapped together to resemble a twisted ladder or 'double helix'. These amino acid strings are made up of nucleotides that are given the letter names of A, C, T and G (adenine, cytosine, thiamine and guanine), connected to bases or the rungs of the ladder. It is the order of the letters that determines the colour of our hair and eyes, our height, and our predisposition to certain diseases. In addition to nuclear DNA there is also genetic material found within the cytoplasm that surrounds the nucleus, mitochondrial DNA.

As we have inherited our DNA from all our ancestors, however distant, they share with us a portion of this information. The closer the relationship, the more similar our DNA will be. It is therefore possible, in theory, to establish family links among individuals and families and even tribes and other indigenous groups.

Of the 23 pairs of chromosomes, 22 are similar, the father supplying one set and the mother the other. The 23rd pair determines the sex: a female has the 23rd pair made up of two X chromosomes (Xcs), whereas a male has one X and one Y chromosome (Xcs and Ycs pair). Therefore, one of the 46 chromosomes in every male is a Ycs. This chromosome is passed almost unchanged from father to son, and any descendant strictly through the male line will have almost identical DNA on his Ycs as his ancestor. Therefore, distant cousins or those with the same surname can prove that they descend from the same male if they have the same Ycs DNA. It was this method that was used to show that President Thomas Jefferson had descendants through Sally Hemmings, one of his slaves.

Mitochondrial DNA (mtDNA) is transmitted from a mother to all her children, both male and female. But it is only passed on through the female line, and so stops with each son. Any individuals sharing mtDNA can therefore say that they descend from a common female ancestor strictly through the female line.

Claims that whereas family historians are only tracing their own family tree, the Human Genome Project is tracing that of humanity may seem far-fetched at the moment, but who can tell what the future will hold.


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