Re: DNA tests

WJhonson@xxxxxxx wrote:

If you are speaking of a Y-chromosone test yes. The Y chromosone only exists in men, not women, and therefore it is only passed from a father to a son. Women don't have it, daughters don't have it.
So it would pass down the exclusively patrilineal line.

On the flip side, mitochondrial DNA is ONLY passed from your mother. Although it passes to all her children, regardless of *their* sex, no contribution is made by the father to this part of the DNA. So this DNA passes down the strictly matrilineal line, although boys have this from their mother, those boys do NOT pass it to their children. The daughters however would pass it to all their children.

There are (extremely) rare cases of documented passage from the father - in the one case I remember clearly, the mother's had a mutation rendering her mitochondria extremely inefficient, and hence even though the zygote starts with a thousand or so from the mother and maybe one from the father, that one paternal mitochondria won out.

On the third hard, your *nuclear* DNA which is what is in the nucleus of your cells, is contributed and mixed together from both parents.

The Y and X chromosomes are also "nuclear". "Autosomal" DNA is the appropriate term for the non-gender-specific nuclear DNA. Exactly half comes from each parent, and exactly half is passed to each child (the material passed being on the average a 50:50 mix of maternal and paternal).

The X represents a special case as well, although not one that is all that useful. A man's X can only have come from his mother, while a woman has one from her father and one from her mother. This means that a woman's will have come exactly 50% from her paternal grandmother, and approximately 25% each from her two maternal grandparents. In turn this provides another 'special' line, represented by alternating genders each generation, which would have provided the highest contribution to the X-chromosome. (This is just a curiousity, though - no beneficial application to genetic testing above what could be learned from an autosomal analysis.)

It is perhaps worth pointing out that because you have 1000 or more copies of the mitochondrial DNA per cell, vs. one (if any) Y, one or two Xs and two of everything else, mtDNA is much easier to detect, and in an old sample, it is much more likely that a copy has survived intact. That is why most 'ancient DNA' work is done on the mitochondrial DNA.

Relevant to this group, there was a recent disappointing report on the potential use of DNA to identifiy the Jamestown burial. For background, following the discovery of the actual site of the original settlement, archeologists located a burial of a seemingly-important individual (based on the location, him being in a lead casket, and the various material found on the body). It had been hypothesized that the corpse may have been that of Bartholemew Gosnold, the now-largely-forgotten driving force behind the plantation. A sister of Gosnold was known to have been buried under the flagging of a Suffolk church, since refloored, and archaeologists were given permission to exhume the site and test DNA to see if it matched that from the Jamestown burial. Unfortunately, based on a physical examination, the skeleton they recovered from the church was concluded not to have belonged to Gosnold's sister, and hence DNA testing was not performed, nor are there any other known matrilineal descendants who could be tested. THis one may remain a puzzle.

taf
.

Relevant Pages
Loading