Y–STR test
To understand what Y–STR tests are, you need to understand two fundamental things, how sex chromosomes work and what ‘STR’ stands for. Let’s start by focussing on chromosomes. Human beings have one pair of sex chromosomes in every cell of their bodies.
While men have one Y chromosome and one X chromosome; women have two X chromosomes instead. In the womb, it's the Y chromosome (the male chromosome) which triggers the development of an embryo in to a male baby. If there is no Y chromosome, then there's a female baby instead (with two X chromosomes in every cell of the child's body.)
STR however, is an acronym for ‘Short Tandem Repeat’ and this is the name given when nucleotides (strings of molecules which line–up to form DNA) are successively sequenced or ‘repeated’ in a pattern through the DNA structures. So, now that you know about chromosomes and short tandem repeating patterns, you can probably see how useful Y–STR tests can sometimes be as paternity tests.
The strings of DNA from one Y chromosome (and adult male) can be compared to strings from another Y chromosome (a child) and a computer or a lab technician looks for repeated sequences which show that the DNA is similar enough for the father and son to be directly related. If there aren’t sufficient repeated sequences or ‘STR’s then the boy and the man must not be father and son because their DNA is too dissimilar. As such, Y–STR tests are a very reliable way to discern whether two male human beings are related to each other.
