Because testing has benefits as well as limitations and risks , the decision about whether to be tested is a personal and complex one.
A geneticist or genetic counselor can help by providing information about the pros and cons of the test and discussing the social and emotional aspects of testing.
Other chapters in Help Me Understand Genetics. Genetics Home Reference has merged with MedlinePlus. Learn more. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. What is genetic testing? From Genetics Home Reference. Genetic testing involves looking for changes in: Genes : Gene tests study DNA sequences to identify variations mutations in genes that can cause or increase the risk of a genetic disorder.
Chromosomes : Chromosomal genetic tests analyze whole chromosomes or long lengths of DNA to see if there are large genetic changes, such as an extra copy of a chromosome, that cause a genetic condition.
Similarly, an individual whose tests come back with a very low estimate of West African ancestry might actually be black. Race is a socially constructed concept. How someone self-identifies in terms of their ethnicity or race may be different than what their genetic ancestry tells us. In fact, our concept of race has such little biological grounding that the Human Genome Diversity Project has opted to avoid using the word entirely.
I still maintain that this is the only way to introduce anything biological or genetic into that discussion. Think about it in terms of science and history. European colonizers invented the concept of race years before the double helix was discovered. Many of their terms for describing human difference, based on traits like skin color and facial features, are still used in our censuses and societies today.
It was backed by men with giant armies, whose objectives were mass enslavement, conquest, and subjugation. In an ironic twist, however, race—and racism—have affected how we understand ancestry. While efforts have been made to produce more geographically representative samples , at-home DNA tests still give far more detailed answers about European ancestry than most other parts of the world. All this leaves us with the question of how we should talk about race as genetic analysis becomes more commercialized and common.
You could very easily purchase one of these kits without coming across it. Consumer genetic testing is growing explosively. According to the MIT Technology Review , 26 million people or more have taken a genetic ancestry test. Tech Review also found that in , the number of tests purchased surpassed sales of all previous years combined. As the market grows, consumers need to be aware of what exactly these tests are telling them and even more so when it comes to information about health and wellness.
Even though genetic ancestry tests deliver precise percentages about our heritage, the reports are best thought of estimates, based on imperfect data. There are about 3 billion base pairs — the individual letter instructions of our genetic code — that make up the human genome. When you spit into a tube and send it off to a company like 23andMe, Ancestry. That would be overkill. All humans have about So instead, to speed up the process, the tests look out for the locations on the genome where people commonly vary from one another.
These are spots where you might have the nucleotide the molecule that forms one half of a base pair adenine and I have thymine. In all, these single-letter changes in our DNA can help explain why one person is taller than another, or why one has brown eyes and another green. Companies can analyze half a million SNPs or more in an ancestry test. When a genetic testing company gets a tube of your saliva in the mail, it first has to extract the DNA from it.
They make copies of your DNA, then break those stands up into shorter chunks. The chunks are then fed into a machine called a genotyping array. These arrays kind of — and this is an absolute simplification — work like a coin sorter, but for SNPs.
Many SNPs are meaningless when it comes to our health. But they can be useful starting points for tracing ancestry. The more SNPs we share in common with another person, the more likely we share a similar, and more recent, ancestry.
Your ancestry is estimated by comparing your SNP results with a genetic database of people with known ancestries more on this in the next section.
But even with that high level of accuracy, when you process 1 million places in the genome, you might get 1, errors. Those small errors alone can help explain why one twin might have slightly different results from another.
This source of error is why the health results you get back from genetic testing companies may show discrepancies too. Errors aside, the genotyping we get from each of the consumer testing companies should be just about identical to one another that is, if the companies are looking at the same set and number of SNPs. But how companies analyze that raw data varies. Companies like 23andMe, Ancestry.
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