Each cell of your body has a copy of the instructions that are used by the cell to maintain and duplicate itself. These instructions (the DNA) are in a single string of only four chemical compounds that are represented by the letters A, C, T, and G. The length of this string - the code - to define an entire human being - is necessarily very long. The human code has 3.165 billion letters. In letter shorthand it looks like:
and so on for 52.75 million lines.
Half of this code comes from your mother, and half from your father, with two exceptions. One exception (only if you are male) is a section of 51 million letters that came only from your father. These are the instructions that make a male different from a female (the y-DNA). The other exception is a string of separate DNA 16,568 letters long (the mtdna). Both males and females have this mtdna, which only comes from their mother.
It is possible, using chemical tests, to 'read' the entire 16,568 letters of mtdna code (a Full Genetic Sequence, or FGS). But it is still a bit expensive. So, depending how much you paid, only a few hundred of the letter sequence may have been read. Your mtdna result looks something like this:
- HVR1 (the basic test): 16223T, 16292T, 16519C
- HVR2 (the extra test): 73G, 189G, 195C, 204C, 207A, 263G, 309.1C, 315.1C
- CR (Coding region, only with the FGS): 709A 750G 1243C 1438G 2706G 3505G 4769G 5046A 5460A 7028T 8251A 8860G 8994A 11674T 11719A 11947G 12414C 12705T 14766T 15326G 15884C
Where a number like 309.1 or 309-1 appears, this means that an extra letter was inserted at that position, compared to the CRS code.
One point of confusion - the Cambridge Reference Sequence is not the code of 'Eve'. Your results are not the changes that you have compared to the maternal ancestor of us all. They are instead the differences between your code and that of a lady who happened to be sequenced in Cambridge, England, in the 1990's. She was actually a member of haplogroup H, the most common in Europe.
Comments? Corrections? Questions? E-mail me!