How do we read your genome?

DNA sequencing allows us to read almost all of the more than three billion letters in your DNA sequence, determine their order, and detect subtle DNA changes or typos at almost every position. When the DNA letters change, it can alter the words within a gene and sometimes the instructions they provide.

Illumina’s sequencing technology does this by breaking the entire genome encyclopedia into smaller fragments of about 200–300 DNA letters each. Since humans are very similar, a reference human genome sequence can be used to help line the fragments up in the correct order. To make sure each individual DNA letter has been read correctly, each fragment is read many, many times.

What is the difference between DNA sequencing and genotyping?

The human genome sequence has about three billion bases, and each cell contains two copies of your DNA sequence, one inherited from your mother and the other from your father. A genotype describes the DNA bases present at a specific location in the two copies. With genotyping, only a certain number (1 to 100,000s) of specific DNA changes are assessed. If new DNA changes are discovered to be important after your genotyping has been completed, you will likely have to be genotyped again to learn about the new information.

With DNA sequencing, an entire sequence of your two copies is decoded. This tells you the order of DNA bases, or letters, over a larger area of the genetic code rather than focusing in on specific locations. In some cases, sequencing is used to look at the genetic code within a single gene. With Illumina Individual Genome Sequencing, we analyze the entire genome sequence. It is possible to reanalyze it in the future for further interpretation as new discoveries are made.