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Parental Testing
By now, it is commonly known that children inherit their parents' genetic traits through DNA. There are small segments of DNA located within specific regions of your chromosomes that vary in size due to repetitive sequences made during DNA replication. Scientists use these regions, termed short tandem repeats (STR), when performing parental DNA testing or forensic DNA analysis. This is done by performing a polymerase chain reaction (PCR) on multiple STR regions. While you could match someone else on a couple of STRs, as you increase the number of tested regions, you will find a unique set of STRs for you. Since your children are half of your genetic makeup, it is therefore expected that they would match to half of your STR regions with the other half coming from the other biological parent.
While analysis is more ideal when both parents submit their DNA to compare to the child's, it not necessary. Only having DNA from one parent will suffice to determine if that parent and child are related. Each person carries two alleles or copies of the STRs. Sometimes, the alleles are actually the same, so it looks like there is a single copy. Regardless, the process of determining if the child is yours is done by identifying all of the parental STRs. Then one by one, the child's STR sets are compared to the parent's STR sets. At least one copy of the child's STRs must match one of the parent's STR copies. The number of matching alleles will tell you how closely related the two people in question are. If they have multiple the same, but do not have a match for all the STRs tested, it is likely they are an aunt/uncle/grandparent/cousin to the child.
Parental testing is definitive. It will determine with certainty that you are the parent. So, make sure that you want the answer before moving forward, because you can't unlearn what you find out. There are cases involving human error in the laboratory where incorrect results were produced. If you ever question results, a second test would be recommended with a different laboratory. Then, cross-check the reports to determine if the labs independently identified the same STR markers.
Relative Testing
It is not only parents that can be tested, but grandparents, aunts/uncles, siblings, and cousins. The overall process is the exact same, DNA samples are required from both parties that are being compared and PCR is performed on the STR regions. The difference is in the number STR regions that match.
Take a grandparent for instance. Let's say a grandma wants to test their grandchild for relative testing. The grandchild is receiving DNA from four different grandparents, two from the mother and two from the father. Therefore, the number of matching STR regions is going to be diminished. This could be alleviated also having the grandparent, parent and grandchild submit samples at the same time, allowing all STRs to be tracked from grandparent to grandchild.
It should also be noted, in some extremely rare circumstances, the grandchild might have none or all of the STRs of one grandparent. Again while rare, it is possible for a parent to pass on the STRs from say the grandma or grandpa only. Therefore, when testing a grandchild against a single grandparent, it could result in a false negative report. To avoid these types of scenarios, it is always better to submit additional samples, like both grandparents and parent or biological aunt/uncle to use for comparisons to the child in question. This provides a wide picture for which to compare and build the genetic family tree.
Ancestry DNA Testing
This section is for educational purposes only.
In today's world of whole genome testing, there is a vast amount of data we can use to look into someone's genetic history. The most common method being used currently is looking at single nucleotide polymorphisms referred to as "SNPs". A SNP is where there has been an alteration in the DNA sequence due to a mismatch pairing due to lack of enzyme integrity (cell division) or due to environmental factors (e.g. sunlight exposure, chemicals).
When examining SNPs for historical genetics, the enzyme integrity during DNA replication is most likely the cause. There are two main places for SNPs to develop for being passed on, 1) early pregnancy when the baby's cells are first starting to develop and 2) during gamete production. Both of these scenarios lead to the SNP being integrated into every single cell of the offspring and therefore passed down to the other offspring. Since human populations where generally isolated in the past with more limited means of travel, these SNPs could build up over generations within certain regions.
Scientists have recently be using these types of markers to determine someone's regional genetic history. They don't have to sequence your entire genome, they will select specific regions that contain known SNP sequences. They can then build a profile based on 100s of SNPs, linking them to different regions of the globe where they are more common and thus more likely to have been passed down from ancestors living in those regions. The reason why they present the ancestorial history in percentages is because it is based on the number of SNPs that matched those regions out of the total number of SNPs they were comparing. It needs to be noted, this explanation is a simplification of the process as a whole and there are additional processes in how comparisons are built that are not easily explained here.
In our lab, we will be looking into providing this as a service. However, this process takes a long time to perform the proper research and development for the methods and analysis.
