Your autosomal DNA test can give 3 billion data points. But does it?

What is Autosomal DNA?

The human genome consists of 23 pairs of chromosomes: 22 of them are non-sex chromosomes and the last pair are the sex chromosomes. The 22 pairs of chromosomes are the autosomes and the DNA that is encoded in them is called the autosomal DNA. So when you take an autosomal DNA test from any of the genetic genealogy companies like AncestryDNA, Family Tree DNA, 23andMe, or MyHeritage DNA, you are getting tested for these 22 pairs of autosomal DNA in addition to X, Y and Mt DNA. The autosomal DNA is inherited from either parent and therefore their occurrences in pairs- one from the mother and the other from the father. They in-turn would have received their genes from your grandparents.

Are there are other types of DNA tests? Which is the best?

Autosomal DNA Versus Mt DNA

As mentioned, there are the sex chromosomes X and Y (X inherited from mother and Y from the father). Generally, if you are a male you would have XY combination and if you are a female, you would have XX. Additionally, there is the Mitochondrial DNA which comes from the organelle, Mitochondria (also known as the powerhouse of the cell). Mitochondrial DNA is small (16,569 base pairs) and is inherited from your mother. Just to give you context, the smallest autosomal chromosome is chromosome 21 and its size is 48 million base pairs. So when you are getting a mitochondrial DNA test (MtDNA test), you are getting your entire mitochondrial genome sequenced.

Autosomal DNA Versus Y-DNA

The Y-DNA test helps in uncovering information about your paternal lineage (father <- grandfather and so on). You can do a genotyping test but for better coverage a full sequencing approach is recommended. The Y chromosome has 59 million base pairs. Many autosomal testing companies use micro-satellites in Y chromosome to determine haplogroups.

What is microarray-based autosomal DNA testing?

Companies like AncestryDNA, 23andMe, FTDNA, MyHeritage and Living DNA perform SNP genotyping (also known as Microarray technique). In this methodology, single DNA bases are read and used to determine who your close relatives (siblings, parents) and distant relatives (second cousins, third cousins, great grandparents etc) are.

How accurate is it?

Whole Genome Sequencing (WGS) is another methodology with which testing companies can sequence every single base pair in your DNA. While this technique is more accurate compared to SNP genotyping, it is also the most expensive. If a book was an analog of your genome, WGS will read the entire book and SNP genotyping will read specific words on certain pages of the book. As you can imagine, WGS is >10x more expensive compared to SNP genotyping.

If higher accuracy is your objective, especially when it comes to health traits, opt for WGS as your DNA test results can give you several more insights that a normal microarray based ancestry test would not.

Using Autosomal DNA in Genetic Genealogy

Mt DNA and Y DNA testing can be used to compute your haplogroups. This information in turn will can throw light on your maternal (female-line) and paternal lineage (male-line) respectively. But if you need to find out about your ethnicity estimates i.e., the percentage of shared DNA segments with a particular population, then companies use autosomal DNA to determine these proportions.

How many SNPs are present in your DNA data?

When you open the DNA raw data file from your ancestry testing companies you can see several thousand lines >600,000. Each of these lines represents a base pair in your genome.

Table source: https://isogg.org/wiki/Autosomal_DNA_testing_comparison_chart

Few things you should know about autosomal DNA transfer

DNA testing companies also provide access to your DNA data. This data belongs to you. You can download this data and keep it on your cloud or local device for reference and future use. You can also upload or transfer your DNA data to other companies to find other DNA matches. But before you go ahead and upload your data, here are few things you might want to consider.

What measures are being taken for data privacy and security?

This is one of the most important things you should consider before performing an autosomal transfer to another third-party website/database. You have to ensure that the website follows certain basic practices in safe-guarding your data. Even websites like Gedmatch and MyHeritage have been victims of security breach in the past.

What DNA data formats does the third-party website accept?

Another big challenge that many genealogy enthusiasts face is the format of DNA data that each company provides. Companies like 23andMe and LivingDNA follow a 4 column format (SNP, Chromosome, Position, Genotype) nomenclature while others like AncestryDNA follow a 5 column format (SNP, Chromosome,Position, Allele 1, Allele 2). Before you upload your DNA data make sure that your format is acceptable. If not, you may have to use some other tools to convert to a specific format before you upload.