GRANDPARENT TO GRANDCHILD DNA TESTING

Grandfather to Grandson, the flow of Y Chromosome DNA

To test if a Grandfather is related to a grandson is very accurate using a Y Chromosome
DNA test.

All men have one Y chromosome which is passed down, generation to generation through their son's. If a Grandfather and a Grandson have the exact same Y chromsome, it supports them having the same
male ancestory (being related).

Because the Y chromosome DNA needs to be exactly the same to support a positive relationship result, the test is highly accurate, above 99.9%.

If you are testing a Granddaughter (females do not have a Y chromsome) then other test types are required. (see below).

Y Chromosome DNA test - Details and cost

For Grandfather to Grandson testing a Y-chromosome test the best option to achieve a high accuracy with relatively low cost. Because all men have one Y chromosome (and females have no Y's). A father will pass his Y chromosome to all his sons. So a Grandfather and Grandson will have the exact same Y chromsome if they are biologically related.

Grandmother to Granddaughter, the flow of X Chromosome DNA

To test if a Grandmother is related to a granddaughter is very accurate using an
X Chromosome DNA test.

All males have one X-chromosome that they have recieved from their Mother. Subsequently, this single maternal X chromosome is passed from father's to daughters. (Son's receive a Y chromosome from their fathers).

So, by testing the two X chromosomes in a grandmother, and the two X chromosomes in the granddaughter, we can determine if they are biologically related by finding if they both have one X chromsome exactly the same.

From the illustration on right, you can see the flow of X chromosome from Grandmother to Granddaughter, via the father.

X Chromosome DNA test - Details and cost

For Grandmother to Granddaughter tests, X-chromosome testing is your least expensive option while obtaining very high accuracy (99.9%+). Men have one X chromosome that they receive from their mother. So, a grandmother will pass one of her X chromosomes to her son (the father), and then the father will pass that X chromosome to his Daugther. Therefore a biologically related Grandmother and Granddaughter will have the exact same X chromosome patterns.