Spit in a tube and we ’ll tell you where you come from : that ’s the introductory premise being offered up by DNA ancestry kit , which have soared in popularity for those who are curious – or who ’ve run out of Christmas present ideas .

We ’ve all heard of the horror stories of people using the kits and find out they ’ve dated their long - miss cousin . Of of course , they do n’t note that in the adverts – but what ’s the realism behind the primary characteristic they market themselves on ? Can one of these trial really tell you if yourancestryisnpercent Irish , West African , or South Asian ?

The way deoxyribonucleic acid testing company start to look ancestry percentages is bycomparingthousands of tiny sections of your desoxyribonucleic acid that often vary between people , known as single nucleotide polymorphisms or SNPs . If we talk about it in terms of those four letters on every high school biology test , in a topographic point of DNA where you might have a letter “ A ” , someone else might have a “ cytosine ” .

These points of variation are compared to those of people in acknowledgment groups , made up of those meant to have “ known ” ancestries – their families have lived in the same place for many ( exact figure seem to be unspecified to the consumer ) generations .

Well , we say comparing ; what they in reality do is look at the particular SNP you have , and then look at how often that same variation pop out up in the various reference groups representing peculiar region . If , for lesson , it shows up 80 pct of the time in the France chemical group , but only 5 per centum in the Russia group , then that part of your desoxyribonucleic acid will be tagged as most likely “ fare ” from France .

That ’s done with each of the hundreds of 1000 of single nucleotide polymorphism used as markers and tallied up . So , when you get an overall event that reads , say , “ 42 percentage – Spain ” , what it means is that 42 percent of those special marking also pop up a decent ball of the clock time in a mathematical group of the great unwashed with “ known ” parentage in that area .

Thing is , the term “ known ” can be give only loosely to these reference groups . First , caller are n’t the clearest about how they watch reference group criteria ; is ancestry self - reported , or do people have to dish out up prescribed records ? Any scientist worth their common salt will tell you that self - reported data is n’t always the most reliable ( although , strangely enough , deoxyribonucleic acid testing can also cast dubiousness on the reliableness of official records ) .

Even if it werereliable , that does n’t signify the people in extension group have inherited the same mutation as their ancestors had . That ’s because we inherit DNA in two half , so you ’re not guarantee to get a particular chunk of it .

“ You start with two parents , then four grandparent , then eight great - grandparent , it goes to 16 , 32 and so on . And by the time you go 10 generations back , there are ancestors from whom you inherit no desoxyribonucleic acid , ” explained geneticist Professor Mark Thomas toThe Guardian .

Then there ’s the matter of how many masses are in each point of reference group – some regions might be better represented than others , so without all the potential information , you ’re not necessarily getting the broad word-painting .

Of course , more people might be bestow over time and that ’s first-class news for mental representation – but it also intend that your percentages might modify over time as the data does , which , if the information above has n’t already , somewhat shatters the illusion that these mental test tell you something mystifying and meaningful about yourself .

Bottom line – these psychometric test are fun , sure , but possibly take the results with a pinch of salt . After all , DNAisn’t all that we were , are , or will be .

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