MRCA generations

[NCroots]

This is a very basic question: when estimating the number of generations to a MRCA, do you include yourself? I always thought you started with your parent and counted up, but I read a blog post where the person was including herself to count generations.

Here's an example... my 2nd cousin & I share a great-grandparent. To determine the number of generation to our MRCA do I count 1- me & my cousin 2- our mothers 3- our grandparents 4- our common great-grandfather (4 generations)

OR, 1- our mothers 2- our grandparents 3- our great-grandfather (3 generations)

I know this is a really rudimentary question, but I've always assumed you did not count yourself.

[Yde]

If I use the TiP-calculator to find a probability that Mr. A and Mr. B share a common ancestor within the last generations ... one get these answers

Generations Percentage
1 4.85%
2 16.03%
3 30.49%
4 45.29%
5 58.60%

Which means that we shall not count ourselves as number 1 when counting ancestors - so the parents are number 1.

But if we count descendants, the children are second generation. There you include yourself.

Or?

[keigh]

Interesting. I always think in terms of steps apart when thinking of a relationship. To me a 2nd cousin is 6 steps apart. That is, from me to my father one step, to my grandfather 2, to my great grandfather 3 who would be our MRCA, down to my grandfather's brother (my grand uncle) would be 4, from him to his son (my father's first cousin) is five and 6 steps down to my 2nd cousin. That gives me a better conceptual idea of how much DNA we might share.