What is a zygosity test?
Since the above definition of an identical or fraternal twin refers only to the similarity or dissimilarity of the twins’ DNA, a zygosity test is a comparison of the DNA between two twins. At Proactive Genetics, we analyze regions of DNA which are called microsatellites. These are stretches of DNA that repeat over and over again, like AACT AACT AACT AACT. All humans have repeating stretches of DNA, and the repeats vary from one individual to another. If several of these repeat regions are the same between two twins, then it is highly probable (i.e., greater than a 99% chance) that they are identical twins. If the twins are different at one or more repeat markers, they are considered to be fraternal twins. Interestingly, these are almost the exact same techniques used in forensics cases where DNA from a suspect is compared to DNA at the crime scene. If the samples are collected in the right way, then this test is very accurate. Indeed, many people have been convicted on DNA evidence alo
