Every cell in a person's body has the same DNA.
Saliva is certainly the most suited and easy to collect biological material to be analysed.
Saliva and DNA samples are collected by rubbing sterile swabs up and down several times inside each cheek.
Back in the "pre-DNA era", blood samples were analysed since the analysis was based on blood groups and other proteins (for example the proteins of the HLA system), which are present almost only in blood.
"Saliva is the biological material of choice
for paternity testing"
