Saturday, July 4, 2009

Snippets and stutters

My title is a fanciful allusion to the two basic entities used in the fascinating domain of family-history research based upon DNA, which has interested me now for several months. There are so many novel concepts and bits of necessary know-how in this field that I've started to set them down in the form of a text, which might one day be of use to other newcomers.

The first thing you discover about this exciting new genealogical tool is that there are two quite different approaches:

-- A female can have her DNA tested to learn about her matriarchal line: that's to say, her mother, her mother's mother, the mother of her mother's mother, and so on. This testing uses mitochondrial DNA, designated in short as mtDNA.

-- A male can have his mtDNA tested in exactly the same way, and the results will be identical to those of his sisters. A male can also have his Y-chromosome tested, to learn about his father, his father's father, the father of his father's father, and so on.

Since a female researcher doesn't have Y-chromosomes, she can't be tested in this second way. But that's not a problem as long as she can call upon either her father, a brother or some other male relative on her paternal side to obtain such Y-chromosome information.

For the moment, personally, I've been tested only at this second level. The results are directly linked to the ancient origins of the Skyvington surname, which is currently being documented.

Let me explain rapidly the sense of my blog title:

-- In a strand of DNA, in a so-called junk region of the molecule (lying outside the coded sections that determine our nature), it can happen that a single letter is suddenly and mysteriously misspelled. For example, a meaningless "word" that has been spelled CAT since time immemorial suddenly reappears, in the DNA of an offspring, with a spelling error: say CGT. An error of this kind is called a single-nucleotide polymorphism [SNP, pronounced snip]. Now, this kind of mutation is extremely rare, but once such a mispelling occurs, the error is reproduced forever after. Some 16 to 18 millennia ago, there was a famous Y-chromosome snip referred to as M343, and one of the fellows with this trivial spelling error in his junk DNA happened to become the great-granddaddy of all of us western Europeans. So, if you find this M343 snip in your DNA, you can be fairly sure that some of your paternal ancestors once spent some time in western Europe.

-- In a strand of DNA, something akin to stuttering takes place when a tiny fragment is repeated several times, for no apparent reason. In a certain individual, a specific instance of such stuttering might involve, say, 14 repetitions, whereas another person might have a count of 13 or maybe 15. This stuttering is called short tandem repeats [STR, pronounced by naming separately each of the three letters: ess-tee-ahr]. Whenever the number of repeats is augmented (suddenly and mysteriously, as for snips, but far more often), the new value is reproduced in descendants of the mutated individual.

Let's leave things there for the moment, because I don't necessarily intend that Antipodes should be transformed into a series of biology lessons. But I'll return rapidly to these subjects, because I've been learning a lot of interesting things, over the last few days, about my paternal snippets and stutters.

No comments:

Post a Comment

Post a Comment