There are 3 major testing options for Grandparent to Grandchild testing:

• To establish whether or not particular grandparents and grandchildren are biologically related
• Grandfather to grandson – Y Chromosome Test
  Men have one Y chromosome, which is passed down to their son and then to their grandson. So testing the Y chromosome will show us If the grandfather and grandson are biologically related.
• Grandmother to granddaughter – X Chromosome Test
  The flow of X chromosome from mother to son to granddaughter means an X chromosome test is more applicable
• Other possibilities
  We can also test other regions of DNA other than X and Y in specific circumstances where the flow of either X or Y DNA is not applicable. A table with the grandparent to grandchild relationships is listed with the cost of each test.

*About Y chromosome DNA testing

To establish whether or not a grandfather and grandson are biologically related, Y-chromosome testing is your least expensive option, nevertheless obtaining a very high accuracy (99.9%+).

Every man has one Y chromosome (women have no Y chromosome). A father passes his Y chromosome to all his sons. Therefore a grandfather and grandson, if biologically related, will have the same Y chromosome DNA patterns.

*About X chromosome tests

To establish whether or not a grandmother and granddaughter are biologically related, X-chromosome testing is your least expensive option, nevertheless obtaining very high accuracy (99.9%+).

A grandmother will pass one of her X chromosomes to her son who will, in turn, pass that X chromosome on to his daughter. Therefore a grandmother and granddaughter, if biologically related, will have exactly the same X chromosome patterns.