Which DNA test to order?

[Nova67]

Hello

I have just transferred my brother's DNA test results from the National Geographic - The Genographic Project - Geno 2.0 to Family Tree DNA in the hope of tracing some common descendants. I have a theory about who a set of my 4th great grandparents might be and am hoping if I can have find some descendants of those families that are willing we be able to submit their DNA also. I have a male first cousin and my mother's cousin's son who are also agreeable to test for comparison.
Does this sound achievable and what testing should I order?
Thanks if anyone can help?
Nova67

[DevonCruwys]

If both the males you propose to test purportedly descend in the direct male line from the same ancestor and therefore share the same surname then they could both take a Y-DNA test. A 37-marker Y-DNA test would be best. Make sure too that you join the relevant surname project.

If they don't share the same surname then both men can take the Family Finder autosomal DNA test but this might not give you the answer you need. Fourth cousins only have a 50% chance of sharing enough DNA in common to show up as a match. Fifth cousins only have about a 10% chance of sharing enough DNA to match each other. See:

https://www.familytreedna.com/learn/autosomal-ancestry/universal-dna-matching/probability-relative-share-enough-dna-family-finder-detect/

[Nova67]

Thank you so much. I appreciate your response. I was hoping you would answer as you are incredibly knowledgeable on this subject.
The link was just what I needed to explain it. One surname interest for the g-g-g-g's is already on the database  (and not the most common name)- it is a long shot.  I thought it best to probably have multiple male relatives test, although would all be same generation. It is looking like a remote possibility.
The people involved were of historical interest in colonial Tasmania - so I would love to know.

[DevonCruwys]

Glad to be of help. There are various geographical projects that might be of interest:

http://www.isogg.org/wiki/Geographical_DNA_projects#Australasian_DNA_projects

[Nova67]

Oh wow - that is great.  Convict and Tasmanian - very relevant! Thanks

[Nova67]

So should I order the Family Finder kits I assume for these purposes?

[Nova67]

So should I order the Family Finder kits I assume for these purposes?

Oops - I think we have already covered this. Tired