Izuna is Sasukes great grandfather.

[Professor Finesser]

If you wanted to prove this you could've said that both where born from the leaders if the Uchiha clan so they're direct descendants of the same bloodline or something, I'm just spitballing here .-.

 

[GrayParadise]

Woah there OP, that's too long. I can't read all of that.

 

[Sourc3sys]

Guys if you think about it, he is right, they both share the same Lastname, proof.

 

[uchihajaime]

They do have a resemblance.
All you need to do his click on the "pictures" when the drop down menu appears click "open in new tab."