Twin siblings can either be 'identical' or 'fraternal'.
Twin Zygosity refers to the genetic relationship between twin siblings.
The Twin Zygosity Test is used to help determine if twins are either fraternal or identical.
When one egg is fertilized by one sperm cell, and then divides and separates, two identical cells will result. These cells will then develop into identical twins.
The DNA profiles for identical twins will be identical. Additionally, the physical attributes of identical twins will seem similar for traits such as hair color, hair texture, eye color, height, and weight.
They must also be of the same sex.
When two eggs are independently fertilized by two different sperm cells, fraternal twins result.
The DNA profiles for fraternal twins will not be identical, and they are just like full-siblings that are born at different times. Furthermore, if the two sperm cells originated from 2 different men then the twins would be like 2 half-siblings.
Additionally, the physical attributes of fraternal twins may not seem similar for traits such as hair color, hair texture, eye color, height, and weight.
They also may not be of the same sex.
Twin Zygosity Testing is used to establish DNA profiles for the twins being tested. If the profiles are different, then the twins are fraternal, and if the profiles are identical then a probability of being identical twins is calculated.
Results are available in 7-10 days after specimens have reached the laboratory.